Well, on my little J31s we use both packs all the time. There are however no checks that both packs are working - either the cabin maintains the correct altitude or it doesn't. Thus in the cruise, I used to slowly reduce the flow from one of the packs and watch the cabin altitude instrumentation. As one pack is capapble of maintaining the correct cabin altitude, I expected to see no change in this. With the correct cabin altitude maintained with one pack turned off, I slowly re-established the flow and then repeated the exercise on the other. From time to time, this would cause the cabin altitude to start to climb. The flow was thus restored immediately, and he failed pack put U/S at the end of the flight.
I found it comforting to know that both my packs were working - thus reducing the passenger discomfort which would otherwise ensue if the only working pack failed unexpectedly in flight!
P.P.