But it is always good to use a few different programs.
That's the main point!
Yes. You will always have progams that will miss certain things. You wil always have programs that remove the wrong things.
In the future, there might be programs that will be 99.9% accurate and precise, but when will that be?
So always have a backup for second opinions. Or... if you're kinda feeling lazy, at the worst, keep some backups or system restore points that are always handy when problems come up.