Ok, you are right about the rhytm stuff (I don't know a lot about the intricaies of music), my bad on that. But I still don't see a reason to add this. You already have an indication of when you miss notes and a sense of pressure that comes with missing a couple in a row. You don't need a special sound or visual to tell you that you are failing.
Also, when you get to higher bom and faster maps, Having any unnecessary distractions can be really annoying when you are trying to conncentrate (at least for me). Which I guess why you would make it toggle-able. But then I don't see why you would want it in the game at all if it is not going to help you improve.