radios are very helpful even if you are sticking together. staying in a group is a good idea for a lot of things, but some people like to go lone wolf. but even if you are staying together a radios helpful. you never want to stay in a tight group because tactically your going to get destroyed. if you are close enough to your group to whisper, then you are close enough to get killed in one spray. radios let you stay organized, and not have to worry about proximity issues. so we can all push foreword, but we are not all right next to each other. say someone sees the guy on your left, and shoots. if you are 10 feet from him, chances are your going to be spotted too. but if you are 30 feet from him you might not have been seen. so if your friend does get lit up, you can engage the enemy. if your too close, the one enemy can keep you both pinned down. if you are far enough apart, he cant cover both of you. this will allow one of you to move and get a shot. radios allow you to do this, and stay in contact with your team without giving away your own position.
or say you do get shot. you head back, respawn, now what? wheres your team? do they know your coming? do you know where they are going? can you connect up with your squad without either A-friendly fire or B- giving away there position or yours?
radios allow you to do this, without causing as many problems. there are still communication problems of course, but it beats the hell out of yelling what your doing.