Another thing to consider is armor. If you are playing a dwarf with beastly armor or Nanok in RtL after a few die upgrades, armor should directly be factored into how useful a health potion is.
A health potion is much more valuable for Corbin with 5/6 armor and damage reduction than someone without armor, as Corbin will in fact benefit from attacks having to bypass that armor and deal the three damage on top of it again, which can often take more than one attack.
The health gained from a health potion is usually gone in one attack on a hero with no armor, but it could take two or three attacks to get a tough hero back to where he was prior to chugging that potion (as inevitably, some attacks won't damage high armor heroes and others will ding him for a point or two), and that's work that an OL doesn't want to waste his time doing if a better opportunity presents itself.
So in these types of situations, that three health can be a real deterrent to the OL's plans, which will probably buy the hero enough time to get to town/get near a hero with a healing item/chug a second potion/etc.