Yet another way assault took it in the shorts in 6th edition is the restrictions on assaulting multiple units. This is a trademark move for Daemon players, but there are restrictions you have to abide by in order to do it legally.
First, you must declare the several units you wish to charge, then nominate the primary target. Then they both get to shoot at you, which is rarely a big deal. If you can reach the primary target, the charge is successful. However, you cannot move a model into base contact with the secondary target if it could reach an unengaged model in the primary target.
Ok, so let's work out how to do this legally with Screamers since they're the trickiest to use. Remember that Screamers are jetbikes and can move over models to get into assault, so it is rather difficult to assault more than one unit with them, though the large size of the model cancels this out to a degree.
Here we have Screamers positioned for a charge against two squads of Mandrakes. I declare a charge against both with the pink unit as the primary. The blue unit is 6" away from the closest Screamer.
As luck would have it, I roll a 7. First I move closest to closest.
Only one Screamer can reach the second squad, so if I want to complete this charge, I can't move it until it is legal to do so. The rules say I can't move a model into base contact with a secondary target if it can reach an unengaged model in the primary target. So, I have to contact every Mandrake that the one Screamer can reach.
Notice that I moved that top screamer into base contact with two Mandrakes at once. This is perfectly legal. Now my one model in charge range is almost free to charge the secondary target.
No model is allowed to finish its move out of coherency, so I can't move it yet. The three Screamers behind it are also bound by the normal charge rules. That is, they must move into base-to-base contact with the enemy if they can. One screamer can do this, so it has to charge the primary unit. In this case, that also brings him close enough to the secondary target that I can finally move my closest model to the secondary target into contact legally. However, if the two squads were so spread out that I had to move my remaining Screamers to maintain coherency, I would have to do that before I moved into base to base contact.
The two remaining Screamers are free to do what I please since neither can move into base contact with either unit. I want them to pile in on the secondary target since the primary target is almost certainly toast, so I move them over there. If the secondary target had been farther away, I would have moved them around the left flank of the primary target to extend 2" coherency, while still being within 2" of a model in base to base contact.
Now I have a much better chance to either stay in combat, or kill two squads with one charge. Most people won't know the rules for multiple assaults by heart because it's rather complex. Just remember to use models that are farther away to cover up as many models in the primary target before you move your model closest to the secondary target. This is very easy to do with Bloodcrushers due to the massive base.
Had I rolled a 10 for charge distance here, it might have been impossible to contact every model in the primary target and still be able to reach the secondary target while maintaining coherency. Think very carefully about the order you move your models or you'll either end up breaking the rules or failing to get the charge results you want.
I don't much care that I have lost 1 attack per model by doing this because I am willing to accept the possibility of a few more casualties in combat if it prevents me from getting shot the following turn. Only horde Orks, Nids, Draigowing and a very few others can bring enough pain in assault to make me consider not going for the disorganized charge.