I would say that the staysail on a cutter is the most useful sail aboard. Not only does it help balance the sailplan, but it also facilitates headsail changes.
If the wind picks up and you need to lower your jib, genoa, or drifter onto the deck, having a staysail set will make your life easier.
Without a staysail, the wind will pull the sail off the deck and into the water. Now you have to wrestle with a wet sail in building winds!
With a staysail present, all you need to do is pull the headsails lazy sheet under the foot of the staysail as you lower the halyard.
The headsail will be pulled up against the staysail and get sucked to the leeward side of it, completely de-powering the sail as it is lowered. As you pull the sail down and under the foot, the sail will come to rest on the deck. Once you have enough of the sail under the staysail's foot, you can drop the rest of the sail with ease and it will fall squarely on the deck and be ready to be tied and bagged.