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.
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.
The best Mac apps for 2020 By Mark Coppock October 9, 2020 If you’ve heard the phrase, “Once you go Mac, you never go back,” you know it holds true.
Best Apps For Apple Mac Pro
Find help or learn more about Professional Apps, including Aperture, Final Cut, Logic Pro, MainStage, Compressor, Motion, Logic Remote and more. The nice feature of this Mac weather app is, these apps can give 3-7 days advanced weather information, sunrise and sunset time. And finally, you can set attractive backgrounds and theme on these Mac Weather Apps to impress your colleagues. Look for the best Mac weather app from the list and have a profound Mac weather in the menu bar. Available for all iOS devices, Todoist is a note-taking and organization app that can keep.
For Safari and Flash, this check is more accurate
Most of those cleaning programs are junk, especially MacKeeper.
Apple Mac Pro For Gaming
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