First of all: I think this skill is very useful and I take it for almost every hero.
Secondly: Orcs are a race whose creeping doesn't depend on external factors (amount of mana per battle, etc.), i.e., they kill as much as they can move in one turn. Logistics with Pathfinding allows them to make much more battles in one turn (especially for machine gunners; you practically need to take Tilshek before the attack. Unless you're going to fight tough enemies right away).
Thirdly: Movement speed and, as an option, forcing the final attack at a moment that is advantageous to you.
Fourthly: Getting +4 to speed during a siege is also a big advantage, because storming a castle is one of the problems for orcs.