There's often situations, usually while sailing "off the the wind" (broad-reach to running) that the driver might not be wanted because it'll make steering more work as it pushes the stern. (weather-helm)
Then there's situations when sailing "on the wind" (broad-reach to close-hauled) when you gotta have it, especially when sailing coast-wise, in bays and harbors, etc.
You'll often see in paintings the tack of the driver pulled up the mast a ways, that's "scandalizing" the sail to reduce it's area with out taking a reef. Another method of scandalizing that's more rare to see is dropping the peak of the gaff. You'll see that more on smallish, gaff headed fishing boats, like catboats and sloops, than on larger ships, mainly because their driver is usually brailed up against the mast and gaff when stowed and dropping the gaff that way would be a p.i.t.a..
There may sometimes be a sail set on the cross-jack, though it's a bit rare. A captain in a rush might have a spare sail hauled up, a bit like setting a stuns'l, but there's almost never a dedicated sail on that yard, and very often there aren't even foot-ropes on it. When the mizzens'l was a lateen, it's spar would have interfered with a sail set on the cro'jack, so a sail wasn't put there.
Into the 1700's, it was quite common for ships to not set a mizzen t'gallant. On many ships t'gallants and royals were set "flying," that is they were already attached to the spar and set from on deck, and brought down, spar and all when taken in. That includes "jack-yard tops'ls" such as commonly seen on schooners, like Baltimore Clippers. Again, much the way stuns'l are set.
While many ships, especially larger warships, had separate topmasts, t'gallant masts, and royal masts; many had t'gallant and royal masts combined in a single spar. Sometimes with, and sometimes without, cross-trees and trestle-trees segregating them. The royal section was usually referred to as the "pole" and the whole spar might be called the "t'gallant pole."