From publisher blurb:
The Campaign Elements series is designed to help judges create persistent campaign worlds, as well as deal with patron quests, divine requests, and the sudden need to “Quest For It”. Whether it is because you are short on players one evening, or the wizard needs to locate a new spell, the Campaign Elements series has you covered.
Each of these areas is short enough to be played through by most groups in only a single session. That doesn't mean that the value of the area is limited to a single session – each adventure includes notes on “squeezing it dry”…effectively getting the maximum re-use from your investment.