Define container; reasonably, a room could be defined as a container. A container of what? And furthermore, define empty! Knowing when something's "empty" has all kinds of applications. That and teleporting, even a few inches could be incredible, especially dependent on how often/quickly you could do it. 3 & 7, hands down
Highly recommend at least trying to poison your data before deactivating/deleting; they have some legalese that gives them a workaround to keep things to an extent