I'm glad the OP is thinking and asking about this.
A screw jack, or any other, the more weight your lifting the harder it is to operate. If you pull the flat up on some kind of ramp, get center of axle as high as normal, then jack, it takes less travel while lifting the load. It also reduces the chance of getting flat off and discovering you are not high enough to get the good back on. And jacking up more, with no wheel in place, is the "best" chance of injury or damage if it falls.
Back in the day, flats where more often. Many, if not most, learned about tire changes before we learned to drive, watching/helping Dad. Now it does not happen often. But I still say everybody should do it on a nice day in the driveway. In the dark, cold rain, traffic rolling past, is not the best time to learn how to do it.
