Boy! I just thought I was in the dark but now I know I'm in the dark about the polyphony.

What's wrong with my thinking here. Someone please explain.

Say you were in a 20 piece band and everyone hit 5 notes at the same exact time. 5X20=100 notes right. I mean somewhere along the line many people will be hitting the same notes right? Just how may instrumens do you have to have play the same notes to make you happy? It seems that some where it would get real cluttered. No?