I was also doubtful of their use as well but have been able to use them effectively. I use them less to inflict damage and more to draw the enemy in the direction i want them.

One tricky maneuver I've been able to pull off a couple times is to have them sprint out in front and get the enemy cavalry to charge. When the enemy cavalry commits I use my own cavalry to swoop in from the flanks and catch them isolated from the main body of infantry. This works well when the enemy doesn't have much cavalry. However, it is sometimes difficult to get them to commit to a charge without getting all your skirmishers trampled.