Action layers

How do I use the layers box in actions?
Is it so simple as every action goes to a different layer or is there some other logic behind it?

For example, I have 2 different states. Both contain actions and I can easily swap between states while in game.

So should I start thinking which action could possibly follow another action and try to put them in subsequent layers?

Should I use same layers for actions that are never going to happen together since they are on different states or will it cause a problem?

Any extra info appreciated. Wanna know more.

I tend to have a layer for each action,

this way you know what layer to do Armature.isPlayingAction(layer) to act like a actuator sensor, and Armature.stopAction(layer) is always stopping the right action only.

Also, it tends to lock up if I ever play two animations on the same layer.