I'm a believer in keeping two sails up on a sloop rig, if you're trying to get above a reach. Small jib, small main keeps things balanced. Large main, no jib, won't give you enough power, and jib alone won't point and gives you lee helm. Beam reach or lower, one sail's okay.
Also, with just main alone in a screecher, it's too easy to get in irons and much harder to get out. That's when you're grateful for the jib.
In the "old days", a storm trysail and storm jib was sometimes called, "a tablecloth and a handkerchief". Not for racing with really, but comfortable and well-balanced. And back then lots of boats didn't have reefing, you'd sail with the jib sort of full, and forward half (or more) of the main luffing. The phrase was (is?), "sailing on jib and battens", or sometimes, "fisherman's reef".
You want your heavy-air sails to be pretty flat, and heavy sailcloth. You can't always achieve that by just roller furling a medium-air genny, nor reefing an everyday mainsail, though with jiffy-reefing you can get it pretty flat. Storm sails need to stand up to a lot of rough use when luffing.