If you aren't talking about something that pertains to the game, you seriously shouldn't be talking. Talking just screws up the focus of a person in the game, because they have to take the time to think about what you are saying. If you are complaining about how bad your teammates are, don't bother unless you give them constructive criticism too.

Even if what you say isn't very harmful, if you keep on saying it, each time your fingers have to move, it slows your reaction time to whatever might happen, so if you get ganked, then you are fucked. That's why unless you are ABSOLUTELY SURE that you are in a safe place to talk, and you are sure that what you have to say is useful or helpful, don't say anything. ANYTHING.

There have been more games lost because of loose lips than because of lesser skill.