It really detects a lot of stuff when you first run it. Is it really safe to delete all this stuff it found with the basic version of the program?
If uncertain, use it's backup option prior to deletion.
I use it almost all the time, and have never had a problem. It may cause trouble if you need to back up data, but I never keep vital data just on my PC.
Most of the time it's fine, very rarely it will delete uncommon registry files that you may need but very rarely as it's always getting updated to not do so.