In 3v3s, though, I have two major schools of thought. First, you can be cohesive, meaning you keep your army together with all your teammates. This is a true team experience, where you try to grind the enemy army down, divide him and conquer him bit by bit. The risk is that you leave your bases open to raids. The advantage is that if one of your opponents splits off and tries to raid, your 3 armies will easily beat the other 2, so the other guy can raid all he wants while you torch his entire base. In a straight-up 3v3 battle, nobody raids, and all 6 armies slug it out; micro and good unit choices decide the day.
In the second approach, you can hold the line with 2 armies, while you go off raiding with the 3rd. I commonly do this when I play Germany, and I've been in many games where the Sioux do this admirably. This is also called the "confuse, weaken and demoralize them to death" approach. The risk is that your enemies will stay together and push on your allies while you are off patrolling some distant gold mine or pine tree. But the advantages are obvious: You can wipe out huge numbers of vils, hampering your enemies' abilities to continue fighting you effectively. Also, because cav is so mobile, you can raid, then respond to your allies' call for help if their battle is not going well. This happens a lot, and the raider gets all the credit. Not only does he kill vils, but then he sweeps in, kills 40 strelets and lets the allies push ahead. Very satisfying when it works.

So what do you think? Is cohesion or raiding the better plan? There are counters to both, but I wanted to get everyone's thoughts on this topic, since we all play so many team games.