That has been my experiences as well.
Contrary to popular belief, Mac OS is susceptible to the same "creeping crud" that other OSes wrestle with. It does a better job than Windows in that regard, but over time the amount space taken up by orphaned files can be significant.
Having said that, I can understand some people being timid to use it. For those, I highly recommend AppCleaner. It is free and does an excellent job with removing files associated with an app that get left behind when simply "dragging and dropping an app icon to the trash".
CleanMyMac went to a single device license so I use AppCleaner on my Macbook Air (CMM is installed on my iMac).