You don't really have to if you don't want to. The potential benefit is slowing down the gradual sagging of the rubber torsion axle, but it won't extend its service life measurably- that's mainly a function of time and/or miles.
I do lift mine if it's going to sit more than a month or so. I take the wheels all the way off the ground, which allows me to spin the bearings occasionally, check the tires
, service brakes
or bearings, work under the trailer... I store it on five points. Two jack stands near the axle carry most of the weight
. Tongue jack and rear stabilizers make it rock solid, which is nice if you use the trailer (guest quarters, man cave...) or work on it while stored.
With a small floor jack it takes less than five minutes to raise it onto the jacks or take it down.