Its nice to know where the opposition is, what they are doing, how many left, and its also nice to tell your team if you are about to do somthing silly.
Communication is one of the MOST important things, it is practically the basis of teamwork, without it, unless you are very close and can anticipate what each other is going to do, you are stuffed! Of course having a game plan would also help, but "no plan ever survives first contact with the enemy".
So basically you need to be able to talk to your team mates so that you know what the hells going on!