To date my experiences with grouping (platoons) in World of Tanks have been . . . less than stellar. My first attempts were made without voice chat, and my friend and I discovered we had absolutely no way to communicate during battle short of the chat everyone on your side can hear. That really wouldn't work. Not to mention typing while trying to drive and aim a turret wasn't likely to work too well, even if that was an option, which it isn't. After a few nights of that we got Skype set up and started using voice chat. That went much better, at least as far as communication went. The match up themselves, well . . . not so much. As Tobold explained in a comment a while back, being in a platoon increases the matchmaking "weight" given to your tanks, thus increasing the likelihood of you being in matches with higher tier enemies. My luck being what it is (if it weren't for bad luck, I'd have no luck at all) we got lots of matches with enemies 4 tiers above us. There's very little you can do in a tier 6 tank against predominately tier 8, 9, and 10 opponents, voice chat or no.
Of course, we've kept playing that way, because having someone to talk to makes it more fun, even if you do spend a lot of time blowing up. We both had lots of tanks, so once we were both destroyed we'd just jump to a new match. It wasn't ALL bad, of course, but overall the matchmaking made it pretty painful. My friend made the comment that he'd never seen such a strong disincentive for grouping in a multiplayer game before. I have to agree.
So it was with some trepidation that last night I grouped up with not one, but two friends in a full platoon and a conference call through Skype. The newest member of our team only had tier 1 tanks (our last miserable outing netting him plenty of xp but very little cash to buy new tanks) so we all equipped ourselves in some tier 1 vehicular goodness (the Russian MS-1) and queued up. The rosters popped up and . . . we got a 50% tier 1, 50% tier 2 battle. That was really quite balanced. All three of us had the 45mm gun on the MS-1 which is more than capable of taking out tier 2 tanks, so we did just fine. We got that same draw, over and over all evening, and quickly started racking up more wins than losses. It was not unusual for the three of us to account for a third or more of all kills scored by our team, despite being in tier 1 tanks. Typically the bulk of the remaining kills would be claimed by Hotchkiss drivers.
Ah, the wretched Hotchkiss. That overpowered tier 2 premium tank was often the bane of our existence, and if ever you saw someone with 4 or more kills on the scoreboard they were invariably driving a Hotchkiss. Our worst moment of the evening came when the three of us were trundling up an alley in our little MS-1s and my tank suddenly exploded. There were no enemies in sight, but clearly somebody had just shot me. My friends continued on, looking to avenge my untimely demise, and shortly uncovered a Hotchkis (otherwise known as a Panzer 38H 735(f)) hiding out behind a shed. My friends had no cover and nowhere to run, so were certainly in a bad position to start, but the enemy's gun never seemed to miss, while our shots went all over, or hardly hurt him. Once the smoke cleared he'd destroyed all three of us. A few moments later he was taken out -- by an allied Hotchkiss (who went on to get 7 kills for the match).
Despite a few setbacks like that, we did really well, and soon my friend was able to buy a shiny new T2 Medium tank. My other friend and I opted for the speedy BT-2. We queued for one final match, and I was sure it was going to get bad now, three tier 2's platooned together? Prepare for the splat! Instead, we got yet another 50/50 T1/T2 matchup. It ended up being a pretty terrible game, with the three of us in unfamiliar tanks, but it was a balanced match and that really surprised me.
So at the low levels at least, World of Tanks can actually be quite balanced and fun even when you're grouped. Who knew?