Actions: On routes or controllers?

I’ve had a look through the documentation but there seems to be very little on the actions hash and the best practice for which type of actions belong on routes and which belong in controllers.

Previously I have seen it said that actions should be placed in the routes where possible but in the getting started guide actions are placed in the controller.

Is there a considered best practice for the placement of actions and should it be mentioned somewhere in the guides?

Here is some related discussion: Best practices for handling actions