All I know is that I'm forever installing and moving and renaming and uninstalling files/programs/whatever, and given how I use the computer, I tend to think that using a Registry Cleaner can be helpful. But I don't know enough to be certain about this.-cyberdiva
All I can tell you is of my own personal experiences. I am a software junkie. If I have a software need (yes, need, dang it!) I will relentlessly search till I have found every program that will fulfill that need & I will end up installing a bunch of those till I finally have the one I consider to be best. I do this for every program I have on my PC. Sadly, it doesn't end there. Every few months I go check out all the new developments in programs and if they look like they can usurp my current choice I install them to give them a try out.
Everything I don't keep, of course, is uninstalled. Compound this phenomena with dabbling in PC games (I'll install games, try them out and after I've beat them or gotten bored with them they are uninstalled) my registry probably has a cubic butt-load of irrelevant obsolete entries.
I never do any registry maintenance and I don't have any program compatibility problems nor does my system run any slower than when I first installed my OS.
Actually, the only problems I have on my system from time to time are those evil little programs you install that covertly commandeer all your file associations behind your back. Fortunately, there aren't as many of those as there used to be and UAC blocks almost all of the remaining offenders.
Side note: Though I have never used it I have heard wonderful things about Total Uninstaller. If someone were looking for something that does what edbro talks about in his post then Total Uninstaller would be the first one I'd try.