Using YOUR vanilla HAs to engage others in melee combat is usually an expensive and bad idea, though, unless the enemy units are infantry archers or infantry javelins.
Yeah, but it's a cheap unit and sometimes turning the tide of the battle with the morale hit for a successful flank outweighs the couple 100 (if that) gold it costs to train another unit. Plus they're speedy, in case the battle gets away form your main force and (like me) you're ADHD and don't follow.