Safe
Safe settings should allow you to continue to use your computer without any noticable difference, but should still clean up your services.
Tweaked
Tweaked disables some real memory killers, but does allow for you to keep things like Glass, etc.
Minimal
Minimal sets your computer to a very optimised state, where all 'fat' services that are not needed for everyday use have been turned off. Using this setting also assumes that you have your own spyware/firewall software.
