MPG has a strong distaste for “system cleanup” software. Here’s a specific case where problems occur, but it is not the only ill that can result. Avoid such “system maintainance” or similar software.
When Apple started shipping Yosemite, we started getting complaints from customers that they couldn't use SoftRAID volumes. We would ask them to reinstall the SoftRAID driver and use other similar tricks, but still the volumes would not mount. After a couple of days of investigation, we discovered that the SoftRAID driver was getting modified.
Yosemite increases the security of Mac OS X by always checking the validity of drivers, any drivers which have been modified will not load. The question was how was our driver getting modified.
We went back to our users and asked them what utility software they had installed. Out of the 6 users who first encountered this problem, all 6 had MacKeeper installed. We asked them to uninstall MacKeeper and download a fresh copy of SoftRAID from our web site. Then we asked them to reinstall the driver using the newly downloaded copy of SoftRAID. After that, all of them were able to mount their SoftRAID volumes.
MPG: MacKeeper was deleting the 32-bit portion of the binary to save space. But that portion is also digitally signed. So the signature check fails, and OS X Yosemite refuses to load the kext.
Any software messing with things like kernel extensions should be taken out to the woodshed. Keep your system lean and clean to avoid problems: install only the things that are absolutely essential.