I have run into a couple of situations where the facing has caused some issues.
1) in my current game, I can't get my single infantry soldier to point away from the tank rolling away from him 75 yards away, he continually chooses to uselessly ping the tank with rifle shots instead of crawling towards the approaching LMG crew on the other side of a hill that he can't see yet. My thought here is that since he can see the tank he won't disengage it.
2) My understanding from reading the forums is that cover arc could result in faster target acquisition. Ran into a situation where i had two tanks in flanking positions to a road. There was hedgerow cover so the enemy tank could not see mine, and a gap in the hedgerow for my tanks to fire atthe road as soon as the enemy tank appeared. Imagine my chagrin as the enemy tank just whizzed by down the road without my tanks getting a chance to fire before it crossed the gap. I had to chase down the tank, which ended up getting to the victory point and demolishing both of my tanks, costing me the game.