I find cavalry useful. It is a quick way to rid your self of enemy artillery. It will draw away infantry from the battle line. Particularly light dragoons are great for putting infantry into a square while they pound them with gunfire and hold them until the infantry arrives. Not to mention what they can do with routers. Also most missile cavalry has better accuracy than line units.

Dragoons, and especially light dragoons are very flexible in battle and often give better than what they get. Just don’t charge them into a square and watch infantry they are attacking to be sure they do not form a square. (that part should be too late to matter irl but in the game having horsemen among the infantry doesn’t matter and the squares are deadly to horsemen. As dragoon types are also excellent for garrisoning cities they are my most used cavalry.

Still half my army is infantry of some sort or other. I like light infantry a lot too. They are worth their weight in gold in the attack. I send them forward of the line to engage the enemy line before the regulars arrive. If the enemy does not close then they take a pounding. If they do then the line is near to take over and the lights move to the wings to continue their damage, but backed up by cavalry. They take higher losses then the line but they are cheaper to build and replace. I usually find three of them a good number to work with.