I too generally use this tactic. Generally taking a minimum of 10 Gangers with my Delaques, my Groups for them tend to be a little bigger than 3 men sometimes.
When I do go with fire teams (although I tend to call them suppression groups) I group them around weapon options.
My Heavy Stubber for instance, tends to get a bodyguard of two or three gangers with lasguns. They provide reliable long range assistance, and give a few closer targets for the enemy to shoot at if I need to break cover.
My second Heavy is a Flamer, who I tend to run with 2 shotgun gangers. As all three can easily ignore terrain cover when firing at foes, it protects the flamer en route to delivering that one decisive blast of flame.
The other party is usually the largest. My gang leader babysits the juves along with however many gangers (usually one initially) that I have hanging around.
The tactic usually works quite well but a good opponent will often exploit it. A gang that sticks together closely will really challenge your convictions of sending in your small groups, especially as it forces you to worry about timing the attacks of your groups to compensate.
When using my Scavvies against groups, I tend to use my bonus 'followers' to hold up one or two of the groups, whilst my main party advances to deal with the others. The main failing is the lack of dedicated support, and as Mastermime says, the main issue with groups is templates.
Saying that, using templates in your fire groups, particularly flamers and Grenade launchers, can counter an opponent who 'walls up' against you.