Pretty much everyone will tell you that, unless you really know what you're doing, don't mess with the registry. Unless you manually messed something up, there is never a reason to touch it. Even then, there's other ways to fix a pc.
There's too much of a chance of breaking something in the registry for no reason.
Whatever you do, dont EVER download a registry tweaker,optimizer, or anything like that. They dont do anything good,and may do more damage than anything.