As for attacking low-AC monsters, I ask for an attack roll if the monster is defending, which makes the outcome uncertain plus there's a meaningful consequence of failure (the monster goes on living).
The meaningful consequence of failing to Hep means your ally doesn’t get advantage and might not succeed in their attack and the monster goes on living. But we digress. The fact that you don’t need to roll means that skills get used less in combat then it could have potentially. I lament this but not enough to actually implement it in my games...probably.