depends on if you're going up agaisnt a army or just defences.

If you're just attacking walls and fortification with hardly any troops then they're very useful combined with a warrior screen and ballistae back up. At higher lvls of walls and defence tech you have to use seige weapons or cataprhacts as using normal infantry or archers it takes forever and lots of losses to bring down the walls and AT's.

Use them if you want but only in certain situations.