It's also everyone's least favourite stance. After about thirty seconds, thigh and calf muscles start to yowl in protest and it becomes exquisitely painful; making students stay down in Sumo is a favourite trick at grading, and the higher your belt the longer you have to stick it out before blessed release.
Last night, sensei Aaron had us hold a Sumo stance for two minutes, while holding a chair out in front of us with straight arms. We did it - because when Sensei says Jump, you say Hai!
At the end of the ordeal, he asked us why he'd made us hold the chair. Because you're an evil sadist, we muttered. No. The point of the chair was to take our minds off the agony in our legs. And it worked, too.
(My favourite stance, since you ask, is of course Nekoashi dachi, Cat stance, in which you stand like a cat.)