Hi there ,

 

If i move my barbarian behind an enemy will it matter? will it be easier to hit or do extra dmg?

 

I currently think it makes no difference unless you are a rogue and you try to backstab.

If you look at the little status icons on your portrait, when there is an enemy on either side of you you get a "flanked" debuff which is a moderate penalty. It is probably worth trying to flank enemies, but only rogues get backstab damage.
 

As long as you aren't suffering disengagment attacks from such movement I think its worth doing.