2tubes
How useful it is in combat depends on the situation and environment. The way I see it its mainly a utility stance, while also touching on combat. Fighting under water can happen, saving on food can matter during long sessions, and regarding the heal, I would make it a group boost on all healing received (healing spells, bard songs or bandage). All heals on any group member is boosted by say 10% or so. The root and snare resistance is also big in some combat situations. So much so that it sounds a bit overpowered.
I think all classes should be quite good at their specialty, and I think this stance reflects an interesting aspect of the LOTR character Aragorn.
The reason I suggest stances is that we can't expect to get it all at once. I'm not sure how I would go about switching stances, but personally I think it makes sense that it takes time to switch, so you typically won't do it during combat. You have to plan ahead so that you are in the right stance at the right situation.
I agree that the idea of "stances" is a bit questionable, but if it can be done smoothly it would give us a nice toolkit.
edit:
Maybe the DPS stance could be dropped and the extra DPS added permanently. That's basically just a balancing question