allows access to certain hidden or unsupported preferences in the MacOS system. Particularly it allows you to make certain changes that other such applications do not. For most of the changes that can be made you must have an administrator account on the system you are running myMac on.
myMac makes changes to your system. In most cases should your system fail to properly function after these changes, you can either undo the change or boot from the install CD and run a permissions repair.