Mac's don't need defragging as OS X automatically writes 2Gb or below sized files to one contiguous space on the drive. There are certain cases where's it's needed to free up a large spaces on the drive, but not something everyone has to do.

Unfortunately, those files take a lot of space on your Mac, and instead of speeding the things up, they slow your computer down. Therefore, if you want to give your system a boost, clean your Mac from the cache files. There are two ways to do that: you can delete them manually or use a MacBook cleaner like CleanMyMac X to do the job for you. CleanMyPC is a powerful PC cleaner tool for Windows that scans your whole computer. Developed by – Systweak Software Price – $4.99 File Size – 1.9 MB Rating–. MacOS Compatibility – OS X 10.7 and higher including Catalina and Big Sur Trial Version – No Available at – Mac App Store. With a plethora of cleaning features, this one is my favorite Mac cleaning app. Disk Clean Pro is the cheapest of all the disk cleanup software & it is priced at $4.99.

Far as other Mac maintainence, there really isn't any except to backup one's files regularly. Keeping Software Updated and run a web browser check to make sure the plug-ins are current.

For Safari and Flash, this check is more accurate

Most of those cleaning programs are junk, especially MacKeeper.

If your friend got onto your computer and visited a bunch of adult sites, then I would recommend something like OnyX, doing ALL the cleaning and maintenance aspects and rebooting, perhaps followed by a Disk Utility Erase free space.

CCleaner beta is out for OS X, used on PC's and combines cleaning and scrubbing of the drive if setup correctly.

If your interested in performance, read my post here

Apple products are made with a variety of materials, and each material might have specific cleaning requirements. To get started, here are some tips that apply to all products:

Use only a soft, lint-free cloth. Avoid abrasive cloths, towels, paper towels, or similar items.
Avoid excessive wiping, which might cause damage.
Unplug all external power sources, devices, and cables.
Keep liquids away from the product, unless otherwise noted for specific products.
Don't get moisture into any openings.
Don't use aerosol sprays, bleaches, or abrasives.
Don't spray cleaners directly onto the item.

Is it OK to use a disinfectant on my Apple product?
Using a 70 percent isopropyl alcohol wipe or Clorox Disinfecting Wipes, you may gently wipe the hard, nonporous surfaces of your Apple product, such as the display, keyboard, or other exterior surfaces. Don't use bleach. Avoid getting moisture in any opening, and don't submerge your Apple product in any cleaning agents. Don't use on fabric or leather surfaces.

If liquid makes its way inside your Apple product, get help from an Apple Authorized Service Provider or Apple Retail Store as soon as possible. Liquid damage isn't covered under the Apple product warranty or AppleCare Protection Plans, but you may have rights under consumer law. If you plan to visit an Apple Retail store, make a reservation at the Genius Bar (available only in some countries and regions).

For more detailed instructions, select your Apple product:

Notebook computers

Learn how to clean your Mac notebook computer.

MacBook, MacBook Pro, and MacBook Air

When cleaning the outside of your MacBook, MacBook Pro, or MacBook Air, first shut down your computer and unplug the power adapter. Then use a damp, soft, lint-free cloth to clean the computer's exterior. Avoid getting moisture in any openings. Do not spray liquid directly on the computer. Don't use aerosol sprays, solvents, abrasives, or cleaners containing hydrogen peroxide that might damage the finish.

To clean the screen on your MacBook, MacBook Pro, or MacBook Air, first shut down the computer and unplug the power adapter. Dampen a soft, lint-free cloth with water only, then use it to clean the computer's screen.

MacBook Pro models from 2016 and later with Touch Bar and Touch ID: Clean the Touch Bar and Touch ID (power button) on these computers the same way you would clean the display. Shut down your Mac and unplug the power adapter. Dampen a soft, lint-free cloth with water only, then use it to clean the Touch Bar and Touch ID.

MacBook (13-inch, Late 2009) and MacBook (13-inch, Mid 2010): The bottom case of these computers uses a soft nonslip material. Use a 3M Gray Microfiber or soft dye-free, lint-free cloth to clean the bottom case.

Desktop computers

Learn how to clean your Mac desktop computer.

Mac Pro, Mac mini, and iMac

If your iMac has nano-texture glass, learn how to clean the nano-texture glass on your Apple display.

First, shut down your Mac and unplug the power cord along with other connected devices. Then use a damp, soft, lint-free cloth to clean the computer's exterior. Avoid getting moisture in any openings. Don't spray liquid directly on the computer. Don't use aerosol sprays, solvents, abrasives, or cleaners containing hydrogen peroxide that might damage the finish.

To clean the display on your iMac, dampen the cloth that came with your iMac—or another clean, soft, lint-free cloth—with water only, and then wipe the screen.

Don't clean the screen of your iMac with a cleaner containing acetone. Use a cleaner intended for use with a screen or display. Never spray cleaner directly on the screen. It might drip inside the display and cause damage.

Displays

If your Apple Pro Display XDR has nano-texture glass, learn how to clean the nano-texture glass on your Apple display. The following guidelines are for cleaning the Apple Thunderbolt Display and previous Apple displays.

First, disconnect the display from power, from its connection to a computer, and from any external devices. Then use the cloth that came with your display or another soft, dry cloth to wipe dust from the screen.

If additional cleaning of the display panel or case is required, use a soft, slightly damp, lint-free cloth. Avoid getting moisture in openings. Don't use window cleaners, household cleaners, aerosol sprays, solvents, ammonia, abrasives, or cleaners containing hydrogen peroxide to clean the display.

Don't clean the screen of your display with a cleaner containing acetone. Use a cleaner intended for use with a screen or display. Never spray cleaner directly on the screen. It might drip inside the display and cause damage.

Peripherals

Apple wireless or USB keyboards, mice, and trackpads

First, power off the device. If your device uses removable batteries, remove the batteries. (If your device is wired, simply unplug it from your computer.)

Next, clean the outside of your device with a lint-free cloth lightly moistened with water. Don't get moisture in any openings or use aerosol sprays, solvents, abrasives, or cleaners containing hydrogen peroxide.

If your Magic Mouse or Magic Mouse 2 isn’t tracking properly, there might be a hair or other debris on the sensor lens. Turn the mouse over and inspect the sensor window using a bright light. If you see debris, use compressed air to gently clean the sensor window.

iPhone cases

iPhone case—silicone

To clean your silicone iPhone case, remove your iPhone from the case. Use a soft, slightly damp, lint-free cloth to wipe the outside and the inside of the iPhone case. Don't use window cleaners, household cleaners, aerosol sprays, solvents, ammonia, abrasives, or cleaners containing hydrogen peroxide to clean the iPhone case.

iPhone case—leather

The leather iPhone case is made from natural leather. Its appearance will change as you use it. It might acquire a patina and might change color due to the oils from your skin and direct sunlight, further enhancing the natural look.

Cleaning the leather iPhone case might aff

Cleaner For Mac Computer