Sephiroths Masamune
Shocodoro Blagshidect
I don't think it can be said better than how rathy Aro said it. Coaching sould be allowed only before and after. It's not like they let people help you in chess, why can you do it in smash?
I always thought it was weird that coaching was allowed. I just wanna say that coaching DOES affect the match and there is NO arguing that. People have won, because they were being coached.
That said, I'll explain why you shouldn't be able to coach during a match. Brawl is a game that has a lot to do with strategy. When you play against someone else you are testing your strategic ability and technical ability versus your opponents strategic and technical ability. When I say strategic ability I'm talking about your knowledge of the metagame (especially the matchup at hand), your ability to read your opponent, your abilty to mix up your style, and anything cognitive. If you have someone feeding your matchup knowledge, reading your opponents patterns for you, reminding you to mix up your approaches, etc how is that fair? Not only can they tell you what to do, but they can tell you what your opponent is trying to do. It really isn't a test of two minds against each other is you add a third party.
An example it illustrate my point: You're a diddy player with a coach and you're playing against a metaknight. Everytime the metaknight grabs you, he down throws you and then waits for your reaction. You're used to airdodging immediately to avoid MK's follow ups (upB), but since he's not doing that he just punishes the airdodge, sometimes with another grab putting you in the same position. The MK grabs you at a high percent and plan to now use his upB after down throw knowing you won't airdodge anymore to get the stock, but your coach is well aware of basic conditioning and is able to think clearly since he isn't playing the match. He warns you to airdodge anyway completely defeating the purpose of the MK's conditioning you for most of the match.
Maybe not the best example, but the point should be pretty clear.
So yeah, coaching only between games. I don't think people really care if you do or don't know how to counterpick, etc. Plus tips in between are fine too, because this is time for you to think about what you did wrong anyway and assess what you should do next. Still I could understand an argument for no coaching at any point of the set.
@above post: you make a good point. A ban on coaching would be hard to enforce imo. If it can be enforced it should be. Or at least you can't have someone sitting right next to you telling you what to do next (which happens all the time).