The way combat works it’s best to focus your attacks and completely eliminate (kill/break) an enemy ASAP rather than just scratch/wound him. In order to do that you must destroy a piece of armor as most weapons aren’t all that good at circumventing it. Spreading your attacks between head and body is detrimental to that purpose, so I’d say head-hunting is a bad idea 90% of the time.
If you want to exploit lack of head armor, use flails – with a guaranteed headbash it works wonders, especially with mastery. If you are after intact armors, use daggers.
9 of the previously-mentioned 10% is on rangers – IF they use a mastered-in crossbow, as they can then 1-shot many enemies regardless of their head gear and previously sustained damage. You were going to shoot them anyway so if you happen to land that sweet headshot it’s a net gain in efficiency.
It is a different story with bows – I frankly fell in love with the perk at first as I tend to build my archers towards the “glass cannon” archetype and it seemed like a foolproof way to increase their killing power. It also seemed very fitting character-wise to build some “hawkeyes” (or Robin Hoods, if you will). However it quickly became obvious that instead of landing several headshots in a row – thus bypassing the usually more durable chest armor and granting a quicker kill – I much more often hit the body, and only land an arrow to the still-armored head when it actually deals less damage than it woukd to the armor-stripped torso.
So, sadly, no Hoods for us – only Tells ;)
The last 1% is for very specific, tailor-made builds, like a Killer with Brute and Duelist using a very well-rolled named 1h weapon – but that’s really more about a self-imposed challenge or min-maxing and not regular play.
On a side note I must admit it saddens me that the awesome fluff (idea) behind high-velocity flying heads is overshadowed by the mundane crunch (mechanics) of the game. Here’s to hoping that the mod support will ne added, so the situation can be somehow… remedied ;)