registerybooster, bugdoctor, etc

I was just wondering if anybody finds programs like this useful. Does the registery get so messed up that one needs a program like this to fix it or else the computer will crash? And do programs like bugdoctor really improve the workings of the computer and prevent crashes and weird things from happening? If the consensus is yes, then I dont mind paying for them to keep my computer from going crazy, but if not, Ill save my money. If there are other programs out there that do these sorts of things that are highly recommended, what are they?