There is a time to speak, and there is a time to shut the fux up and shoot back for your dear life.
Middle of enemy territory/battlefield/area that is most obviously unsafe is not the place to talk. Go back to your own lines or death if you want to hold a lengthy conversation.
Admittedly, group coordination via teamchat is useful, but more often then not it's easier to hope people get the impression of charging in behind you then leaving yourself open to the critter or person around the corner for 3 nanoseconds.