PRAM holds your personal settings for some of the basic functions of your system. PRAM, like other preference files can be subject to corruption or bad data more than other types of files because they are basically in constant use. If you have a preference in your 'Preferences' folder that goes bad you can usually just throw it in the trash and the application will make a new one for you the next time you use that application. PRAM functions in a similar way, if it for some reason gets corrupted there is a relatively simple process of erasing it and thus removing any bad data. The first part of the answer to this question is that you never need to clear out your PRAM unless there is a reason.
Some people make a habit of clearing their PRAM every few weeks or once a month.
There is nothing wrong with this practice but generally with corrupted PRAM your problems will be more serious and apparent like your Mac won't start up or you couldn't use your printer. I'll start with my personal experience. Usually the type of problems that can be related to PRAM are ones that have to do with the things of which the PRAM keeps track. The logic is simple, no power means no memory and your computer just forgets. The second most likely situation is that your computer will just refuse to do anything at all when you try to turn it on.