I've seen wedges charge right through an enemy unit (though usually a routing one) and then comes around for another charge, while a line charges once and then gets caught in melee.

I use a line a lot more often, though -- much better for chasing when the opposition routs. I normally use wedges for squeezing through some gap that appear. For instance, if there's a big brawl around an enemy general, I'll sometimes form a wedge and ride around. A wedge is less likely to get hung up in melee combat while trying to ride around units or through a gap.