The Ranger's Command ablity states:

"When you work with your animal companion on something it’s trained in…" and then you get a bonus based on the stats you've chosen for your companion.

So, for example, if a companion is not trained to fight monsters, it cannot add/absorb damage for you if you're fighting a dragon.

That makes sense, however, it seems that the Commadn ability has no use for some of the training options. For instance, is there any Command that you can use when you work together with your companion at Labor, Guarding or Performance?

Also, can a companion be sent to do things it is not trained in? For example, can a Ranger leave his wolf to guard the entrance of the dungeon if it does not have guard training?