So if you notice crab aliens are pretty smart as when they reach their final position they will rotate their facing in order to expose their highest armor to where you are. Again, pretty smart.
But! How can your soldiers change facing at the end of a move? Shouldn’t we also be allowed to?
Not too sure how the arthrons do that. I mind controlled one once and tried to set its shield up to block some hostile fire… made mine turn the wrong way. UI for that shield block is awful. I don’t think there is any way to do that for our guys, but based on my arthron experiment… Well i hope the design it better than the shield blocking if they put it in.
Storm Guard Darkness is Coming has a great rules set where facing is important, and the design found how managing it reasonably without burdening more each soldier action by a facing choice at end of soldier turn.
In PP a lot of facing is removed by cover, and seem use the same trick except that most often it is invalidated by cover or because you end with a move.
Facing is defined by last attack and it becomes more clear with the vehicles with guns. Cover broke it, and when it becomes a tactical tool in SGDC because it is close range and because you end with attack, it lost its meaning in PP because of shooting and because of the great flexibility on how you manage a turn that is often move shoot and move.
I’d say that soldiers aren’t like crabs and much more symmetrical, cover matter more, facing not much, and they don’t have shield. It’s not worth burdening the gameplay fluidity.
If your soldier lost the armor on his right side, for example, it would be very important to make him face with the left side that still had armor. If you design a system with multiple body part targeting and separate armor values than yes facing IS very important.
UFO Defense has facing and i don’t see how it burdens fluidity at all. It is just one mouse click.
I thought there was a keybind for facing but can’t find it. Such a pain when it comes to vehicles that are zero point turn but you can’t turn them without driving forward. I’ve also had overwatch not fire because the soldier was crouched behind cover facing opposite the cone.
For vehicle I take care keep last move to choose the direction so the facing, soldier should allow the same, but when in cover it’s more complicated.
From what I know you don’t change facing. Developers for some reason though that setting soldier to face closest enemy will be the best option… 
I think it would be very useful to have a way to at least change the vehicles’ facing direction while your turn is active.
Vehicles are big, they are going to get hit no matter the distance the enemy is shooting from.
Eventually, MGs are going to shred all its armor.
Why wouldn’t we be allowed to change its facing direction directly to whatever position we want since it’s already possible to do by aiming at enemies?
It’s either: Allow for free rotation or just lock the vehicle in place and only allow the vehicle’s weapon to rotate, that would make a lot more sense but not as fun, so hush… xD
Since I use the Armadillo as a mobile cover (Not sure about you guys), a few situations I find myself in are:
Vehicle blocking my Snipers’ line of sight to enemies stacked up around it by so little, So I keep going back and forth aiming at different enemies with the Vehicle until I get a good angle with the Snipers.
Wanting to point the vehicle’s front to silent Triton snipers, gotta use APs to move the vehicle since I can’t see the Triton to aim at it directly.
Can’t move the vehicle back and forth to expose its front to the enemies that are moving in on their next turn since I have units sitting behind the vehicle for cover already.
As for soldiers I don’t mind if it wouldn’t be a thing but I gotta say I’ve actually felt the need to face another way from time to time, and it has always been the same situation: My Heavy getting huge hits at his weapons while behind cover and I’m not able to keep them from sticking out of cover for incoming turns lol
Keep the last move bit to choose direction, and yes with some vehicle it means you can’t attack twice, it’s a deal. But if you attack twice you can at least choose your last attack according to best possible facing.
Unfortunately you can’t change your facing, the game takes a very streamlined approach to how you can control your soldiers around the battlefield in the normal ways that you’d expect from a TBS game. (No change of stance or aiming mode either.)
Soldiers also have 360 degree vision, they literally seeing things out of the back of their heads.