Some people say it is better to avoid using cleaning utilities as they may harm your system and make your Mac software work incorrectly. However, in case of CleanMyMac that is not true. Here is the list of files CleanMyMac can safely delete from your Mac:
Caches and logs. Cache files speed up loading content by applications. However, they often become corrupt due to conflicts, unexpected quits and software updates and need to be cleaned in order to keep the system optimized. Logs can also be deleted with no harm as they are generated for debugging purposes only and unnecessary for home users.
Language Files. Mac OS X and most of the apps are presented in a dozen of languages. But most users prefer to use only one or two languages. CleanMyMac can easily delete unnecessary language files and free some space on your Mac.
Universal Binaries. In order to support both Intel and PowerPC architectures many applications contain Universal binaries. Since you use only one architecture code, there is no need to waste your disk space on a code for another architecture support, which can be found in these universal binaries.
System Junk. Mac OS X and Mac software at large generate many files (such as .DS_Store, .Spotlight-V100 and others) for debugging purposes only. Such files can be deleted with no harm to your applications.
Trashes & Leftovers. Every deleted widget, application and broken preference pane can leave leftovers in your system. Such files, along with data in Trashes (including iPhoto Trash) are unnecessary and can also be removed.
iPhoto supporting files. If you keep your photo collection in iPhoto, then most probably it is full of supporting files that take up to 15-25% of your entire library. These supporting files include photos that have been already modified or automatically rotated, duplicates and others. CleanMyMac can easily find and delete those files without affecting you photo library.
As you see, CleanMyMac knows how to clean a Mac from different types of unnecessary files and Mac software harmlessly.