Facing changes are free but are important. As far as movement goes, a unit's facing at the start of their movement can be changed for free, so it truly has NO effect on the direction that they can move. At the end of their movement, facing is again without movement cost BUT will determine what targets may be senn throught the rest of the turn (for attack/line of sight and defensive purposes).
Short form: facing is important for attack and defense, buit does not truly affect movement at all.
As far as unit's blocking the movement of other units.
Yes, they do. Any enemy unit automatically blocks the passage of a friendly unit. In fact, as melee combat range is 2", any Fuzzy Hero attempting to move around an enemy must skirt said enemy by at least a margin of 2" (or more). One of the reasons that we recommend the use of tape measures is so that the tape can be bent around the opposition unit, thus giving a true measurement of the distance required.
This draing is a bit crude - but I hope it helps:
The guy that runs this chicken outfit.