I don't use cavalry much for bridge battles, especially if I'm the attacker. When defending bridges, I sometimes allow the attacker to cross with some of his men, and then hit him on three sides. I do this more often when I don't have any strong defensive unit available, and all I have is spearmen and the like. Cav can be very useful in these types of situations.

In hilly & mountainous terrain, I find cavalry to be of limited effectiveness when I'm the attacker, but they still have their uses. The best thing I can usually do with them is get my horse on high ground in an attempt to force the defender to abandon his current position for one that gives him less of an advantage.

On mostly flat terrain, however, cavalry is king (of course). And when I play as the Spanish (which is often), I *always* field large numbers of Jinnettes.