Maybe this would be a better question to ask the game designers about why we have a health (HP) and endurance. I find it rather confusing in battle when I am pausing and making choices how to advance through each in counter. Does anyone else feel the same way? Can someone explain to me why they made this choice, was it because of the people at WOTC and PAIZO Publishing not allowing them to simply use HP instead of this mixed system. Can this feature be removed if enough people complain about it?
The only thing you need to concern yourself with - in battle - is pretty much just Endurance. Endurance is what matters within a battle, whereas Health is something you should concern yourself with from rest to rest. In essence, it's the difference between "tactics" and "strategy." Within one battle, you need tactics to manage how your characters are dealing with their Endurance. Across many battles, you need to make sure that health loss is being shared in a way s.t. you won't be out of camping supplies when you most need it.
The only time you have to worry about Health and Endurance at the same time is if you've gone far enough without rest that you have a character who's been taking a lot of damage that they have less health remaining than endurance. And in that case, it's still not too bad because by default the character won't die the first time they hit 0 health, they'll just be knocked out and then maimed.
Personally, I love the Health/Endurance system. It solves several interrelated tedium for many other similar games:
1) time spent doing nothing but healing. This was the worst thing about the original Baldur's Gate (since a lack of "Heal on Rest" meant you *had* to spam Cure Light Wounds all the time) and several other games (like having to sit down and eat food in World of Warcraft). You (generally) only need to worry about your characters' fighting capacity *in combat* since outside of combat they regenerate Endurance so quickly they'll be at full Endurance for the next fight.
2) Absolutely needing dedicated healers. Any game system that *requires* you to have a specific role reeks of a broken game system, IMO, and it's because of inertia and nostalgia that we tolerate so many games where you can swap out fighter/rogue/mage-types, but generally always need a priest-type. Now, intelligent "aggro" management will get you through any one batle, and the rapid out-of-combat endurance regeneration takes care of the rest.
3) Rest-spamming. You don't need to rest-spam anymore (and not only because it's impossble due to limited camping supplies), and you're encouraged--in a way not done so in most other RPGs--to intelligently manage your character's abilities and how much damage they're taking in combat because--while they'll almost always be at full endurance for any given fight, their health provides a long-term cap on their effectiveness. I.E. if you run every battle MMO-style and let BB-fighter take all the damage, you'll find you need to rest when most of your party still has most of their abilities left (and you'll be running down your campign supplies rapidly). On the other hand, if you're able to switch out who takes punishment (i.e. to another tank-like character or even your BB Priest or BB Rogue at times) and balance out the damage, you'll be able to go a lot futher betwen rests.