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.
A best mac cleaning software offers versatility in its tools and has modules to perform overall Mac cleaning and optimization by removing redundant files to clearing of temporary logs. Smart Mac Care is the best Mac cleaner app to keep your system protected. https://gamingever491.weebly.com/how-to-download-iphone-apps-to-your-mac.html. In this article, we will discuss the best free cleaning apps for iOS devices i.e. IPhone and iPad in 2020. Deleting redundant files, junk files, temporary files, caches, and cookies is the best way to clean and optimize your iPhone and iPad.
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.
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.
Free App To Clean Mac
CCleaner beta is out for OS X, used on PC's and combines cleaning and scrubbing of the drive if setup correctly.
Best App To Clean Up Macbook
If your interested in performance, read my post here