Really good, succinct, run-down, I love it.
While we’re building up explanations, I’ll add my own, the casual one I usually give people:
Marking stake as Online means: hey, network, expect to hear votes and stuff from my running node, send me votes and blocks and I’ll think about them, etc.
Marking stake as Offline is like putting up a Gone Fishing sign: it’s helpful to the network to know that you won’t be around to vote on stuff, that your stake shouldn’t be used when calculating majorities, and stuff like that.