Aldarion
Archmage
Heavy cavalry as shock troops are only one tactical use for knights. The mobility alone is an extremely important factor. As long as you have formations, striking the enemy from the wrong direction is always devastating. In modern warfare, when soldiers get surrounded, they are unable to move to different positions and to be resupplied, but they can still fight. When a formation gets flanked, there is almost no chance to resist and fight back. That's why ancient and medieval commanders always loved rivers and thick forest on their wings.
That is why infantry square was so popular. Spanish tercio is maybe the best-known pre-18th-century variant, but Byzantines utilized hollow square as one of their basic tactical formations (with cavalry and supplies being protected within the square by infantry), Crusaders picked it up from them, and both John Hunyadi and Matthias Corvinus also utilized similar formation.