Yes, the alt+left click charge is a very good idea to use with cavalry. If they have a secondary weapon, they'll charge with their primary* (which usually has a better charge value) and then switch to the secondary (which is usually better in melee). It's good both for the few seconds they're in melee when you use them as a hammer, and especially when fighting other cavalry. It's just too bad the AI doesn't use it, though.

*If their primary weapon is ranged, be it as a prec or not, they'll charge with their secondary instead.