My knowledge is theoretical as I've never actually sailed on one. But I hope to soon, I have a plan!
I've been out for a day sail on one. The volume below decks is huge!
the sail can be depowered by raising the sprit - and with a big winch, that can be done by just one person. Better than our barge, where it takes hercules to even raise the sail, or two people on the winch. Not that we ever sail it.
Isn't there a way of brailing the mains'l up to depower it ?
You can do that as well - but the sail is effectively in two sections. Raising the sprit 'flops' the section between sprit and mast. The section below the sprit can be pulled up to the sprit.
It looks awfully messy compared to a gaff or bermuda rig but allows for tuning of the sails very easily. With the little sail at the rear mast and the foresails the boat can be depowered and steered just with the sails. Leeboards allow you to tune the centre of turning to match the sail arrangement.
Humber Keels had something more like a 'viking square rig' and brailed the sails up to the yard, but the effect was similar in that only two people were needed to handle the boat.