I tend to use wedge mostly for manuoevring - especially horse archers that have gone and "skirmished" themselves into a tight spot and need to get out of harm's way. It's also handy for rear-charging a pinned unit. I also have used the three-way wedge for bridge defences where I've had more cavalry than heavy infantry. Cav aren't so good for plugging a bridge but a good three-way wedge when the enemy first set foot on my side can have them running away quite nicely It's also good for charging shock troops through castle gates/breaches.

As for the general always being in the van, I don't believe this is the case. AFAIK it is the highest valour men in the van, and if the general is low valour, he'll be further back. Evidence for this being the position of the unit flag, often in wedge formation, this is in the rear ranks.