What it's for
A quick, unbiased way to decide who goes first - in a standup, a retro round-robin, or picking who presents first in a demo. Nothing more complicated than that.
Why random beats "whoever volunteers"
Letting the same confident person always go first in a discussion (like Scrum Poker's reveal order) tends to anchor everyone who follows them. A genuinely random order removes that bias without anyone having to think about it.