I would add to what Ogrob has said some considerations:
- Cavalry is now more maneuverable than before.
- Javelin and composite bow armed mounted units are very flexible and dangerous, particularly when combined with battleboards abilities. For instance, in the Norman battleboard allows you to activate all your mounted units interrupting enemy activation. If armed with javelins and well placed in the tabletop, you can wait until the last activation of your opponent, then activate your mounted units up to M; use your free shot -shooting with javelins or composite bows can be activated as free activations that don't generate fatigue- and then, in your turn, move out of charge enemy range. Byzantines can use similar tactics with their composite bow armed mounted Hearthguard.
What you need to keep in mind though is that mounted units will work better in armies that were, historically, strong in cavalry -Byzantines, Normans and Carolingians-, as their battleboards will reward tactics better fit to mounted units.