I mean.. Nowadays there are way too many variables, champions and mechanics to consider and it's very unlikely that your single ban would have a decent impact on the gameplay. It seems to me that this feature is a bit random, at least for non professional players or high elo players.
All in all bans are made before champion select, you dont know who are your enemies and what are they going to pick. And usually for all of us there are more than one champion you are not comfortable to play against. The only useful thing you can do is to ban the main counter of the champion you are going to play, if you have any in mind. But... is it worth it? Will it change the game that much? Personally i don't think so.