I always move on to another pitch after an hour (maybe a bit longer if the money's good and no one's waiting.) It makes sense basically, because i can't play for more than two hours without repeating myself unless I really strain for tunes I've more or less forgotten or never polished up and the shopkeepers/locals get bored if you're playing the same thing over and over again. I try to give other performers space especially if they're playing quieter instruments. Most of it's common sense and common decency.
If people infringe on my pitch with loud instuments I'll compete generally. (I'm a fiddler, but my fiddle's got BALLS! Gave a gaita player a bit of shock in northern spain once- I wasn't playing louder than him, but it was loud enough to make a musical mess and there was no way people were going to pay either of us for the ensuing cacophony.) Still, sometimes there's no option but to move on. Just like the cities. You can get away with unlicensed busking sometimes, but if the police are going to be real bastartds about it, you move on and wish a boring day to day life on the people who banned busking in the first place.