If you really want to see what happens (or if it will even let you), set up a test environment and test. Realistically as others have pointed out, there is no gain to doing so and I can't imagine your AD being so inundated with objects that the few built-in groups/ users really make a difference. If you have your AD setup with proper OU structure you shouldn't really see these objects on a regular basis...
As far as what it will affect, read up on the AdminSDHolder object. There is a process that runs that checks the ACLs of objects that are members of Protected (built-in) groups against the AdminSDHolder object and overwrites changes made to the objects with that of the AdminSDHolder object. If you were somehow able to delete those groups, I imagine you'd have problems on your PDC Emulator FSMO Role Holder, where this background operation runs (every hour).
Additionally, those built-in groups logically correspond to the local built-in groups on your DCs.
It's probably best that you don't try deleting them as they are there for a reason.