If a blueprint is placed in a logistic network (only then), all entities that can't be delivered are automatically downgraded to the lowest tier that the logistic network can satisfy. Upon constructed by a robot, the low tier entity will be marked for upgrade to the original tier.

That way you don't need to store your blueprints in the lowest tier or don't need to to downgrade them manually in early game. When ready, you have the entities already marked for upgrade.

Also provides a shortcut to switch behaviour, which upgrades entities instead of downgrading them