Yari cav is the only cav that has some uses as it gets a charge bonus. If I have cav, I try to use them like a wrecking ball, once the entire, or most of the enemy army is engaged.
As others have said before, for me to get more out of cav, I'd have to adopt a different play style and I am usually very infantry focused.

Another thing that annoys me about cav is that it is very expensive. You can get 2-3 units of Yaris for 1 unit of cav and that unit of cav is never going to outperform 3 units of Yaris, unless you are having a race.