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.
Similar Photo Cleaner comes with a plethora of powerful photo organizing features that are incomparable to any other similar tools available in the industry. With easy-to-manage interface & smart duplicate photo cleaning tools, Similar Photo Cleaner is undoubtedly the best duplicate photo remover for windows 10 that you cannot afford to miss.
Use a duplicate photo finder to clean up your Photos. First, you need to find duplicate photographs in your gallery. Then you have to figure out which version to delete in each case. All that takes loads of time if done manually, and Gemini 2 does 90% of the work for you. To find duplicate photos on your Mac, do the following. Duplicate Photo Cleaner is a powerful tool that helps you find and remove duplicate photos from your PC or Mac. With this program you can easily organize your photo collection and remove duplicates or similar images. Duplicate Photo Cleaner has three scanning modes - Standard Scan, iPhoto Scan and Sector Detail Scan.
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.
Similar Photo Cleaner Mac App
Similar Photo Cleaner Mac App
For Safari and Flash, this check is more accurate
What Is Similar Photo Cleaner
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.
Mac Cleaner App
If your interested in performance, read my post here