In warband (and some of the battle tests I’ve done) I generally keep my cav in a safe flanking position until they can be used to charge in on an engaged enemy infantry group from behind. (For background I prefer Sturgia). I generally divide my army into 4 divisions: two infantry lines (either both heavy infantry, or front line heavy infantry and secondary line skirmishers (like berserkers). 1 archer line, and a cav unit directly under my control. Archers stand in front and fire a few volleys until enemy gets close and then they fall behind inf lines. Front line heavy inf operates under shield wall order (acting as anvil for later cav charge) and secondary line operates under “line” formation command. With the AI as it is currently, this behavior allows them to break formation slightly and skirmish out from behind the shield wall heavy inf. Currently does not work well with berserker type units as their weapons get caught up in shields. Hopefully that gets fixed. But regardless, once enemy inf is engaged with front line, I ride out on a flank, turn, and charge, ideally crushing enemy between cav and shield wall. The only other time I might use cav is to counter an enemy cav charge against one of my inf flanks. But that can lead to quite a few losses so I try to avoid that if possible.
