That doesn't make capturing foes any more inconvenient for players (like me) who memorise exactly how many hp has been lost by everything on the board.
It still makes a difference. In fact I expect my players to track HP and apply the half-damage only on the final blow. But...there comes a point in the lifespan of many bad guys where half-damage can mean the difference between dropping them and letting them live for another round, which can in turn make the combat more difficult, especially if you need to capture multiple foes.
In our last session the group had to capture 3 gnomes to feed to a witch (don't ask), and as they fought, I let them make Heal checks to estimate how many HP the bad guys had left. Even with this knowledge it was a gamble: often they would deal half-damage for the killing blow... only to roll low and fail to drop the guy. Once the rogue critted and one-shotted a gnome; HP tracking didn't help there.
They managed to bag 3 of the gnomes, though. The goal isn't to make capture impossible or even difficult, just slightly harder than killing, so that it becomes a strategic decision rather than a standard operating procedure.
-- 77IM