How important is it to know to play a given song in multiple keys? I'm not talking about anything too complex. Think pop songs or traditional songs like Amazing Grace, Silent night, etc.
Say if I can only play these songs in a single key is that "bad"? Can accomplished musicians play these songs on any key they feel like? And on the fly ... meaning no practice beforehand, and it just sounds good?
note: I can play any of these songs with practice on different keys. but I'm talking about real-time, on the fly, type playing here, where it sounds good the moment you change keys.
another note: my purpose is being able to jam with other musicians, improvisation, busking, etc.