What you don't want is to totally ignore the calvary or slingers trying to get around your flanks. Someone better get on them. This leads to interesting decisions.
Maybe those cannon up on the ridge are a serious enough threat that you'll charge them anyway, even though that leaves the infantry on their left free to wheel into your flanks. But in return for taking those cannon out, your guys are going to get hit hard.
Of course, "hit hard" is relative. If the foes are a dragon and his 9 common kobolds, you might prefer +50% or +100% damage from the kobolds over several rounds to letting the dragon last any longer than absolutely necessary. Or you might not. Or you might be ok with that once you've whittled them down to 4 kobolds. Or you were ok with it, until the dragon cast a spell on the kobolds and made them hit that much harder. Thing is, most of the time, you do have a decision to make. It isn't, "duh, dragon, kill it!"
I don't know of
any real-world
or story-based combat situation where some thoughtful participants thought it was a good idea to let any competent combatant run free for any length of time--except the ones in RPGs or clearly derived from them. There are a few instances were it was deemed a "lesser, necessary evil" than the alternatives available, but not "good".