Last time I talked about HP structure in DnD Next and I suggested that they really need to have a system where there are Hit Points that regenerate quickly after combat and represent fatigue and Wounds that represent actual trauma and which you only take after your Hit Points are depleted. Sthenno suggested some problems with that system in the comments and I wanted to talk about that a little specifically looking at the Hit Point system I developed for Heroes By Trade.
The primary issue Sthenno brought up is definitely real - when you all have Hit Points that come back after a fight there is a real issue that some fights don't damage the characters at all. It is easy to imagine going through a combat that should in theory be challenging and coming out the other side without using any permanent resources. This can be an problem in two ways: First, the characters may not feel challenged if they don't actually get hurt. Second, it is very difficult to drain the resources of the characters over several combats since if you make a fight hard enough to do Wound damage you could easily end up killing off characters.
I don't think the characters not being challenged ends up being an issue most of the time. In the tests I have done people recognize that take Wound damage is a really big deal and they get very worried when they get low on Hit Points. Even if they end up coming out without a scratch the concern and/or fear they felt at being hit seemed plenty real. The other factor that works well in this case is that in Heroes By Trade there are a variety of defensive actions characters can perform. When someone gets low on Hit Points they don't just keep on swinging and hope; rather they can take the simple but effective Defend action or they can use Powers that let them run away, be harder to hurt, or restore their HP. Getting into a situation where you feel the need to use your defensive abilities to survive is a good way to make people feel challenged and afraid even if they end up winning handily.
The second issue of draining resources is a trickier one because it relies so heavily on GM style. Some people like me tend to write more story based combats that are spaced out. Characters get into fights because they have to or because they want to achieve specific objectives. I don't design gigantic dungeons that involve dozens of fights against forgettable opponents. Because of this draining their resources simply isn't something I think about fights doing since the characters generally have ample time to rest and recover before the next time they have to fight again. I just don't rely on that mechanic.
However some people do want to drain resources so in that sort of case there are a few arguments in favour of HBT's system. The Powers characters use in fights can all be Augmented. Augmenting a Power costs a variable number of Wound Points and makes the Power drastically more effective. As an example, Arcing Bolt shoots one enemy with lightning but if you take 1d6 Wound damage you get to shoot three enemies instead. Characters very often end up spending their Wound Points to do really nasty things in fights and take damage without the enemies having to actually chop through all of their Hit Points first. Certainly characters *could* refuse to Augment their Powers and in fact may often do so when an encounter seems trivial or is going really well but in most cases fights end with people having spent their resources of their own accord. The temptation to do something really cool in combat and take damage to do so seems irresistible to players... which of course was exactly what I was hoping for.
I should note that DnD Next doesn't have the same mechanics and thus would probably have a lot more issues with switching to a HP/Wound system. There aren't effective ways for characters to defend themselves, the system is designed around depleting resources with trivial and boring fights, and characters cannot spend their own resources to do cool things. I still think all of the current ideas DnD Next has for HP are terrible but it may well be that given their constraints they are simply going to randomly pick a terrible option and go with that because they don't have a way to build a good option instead.