Here's the war academy article on mobilization.
Yeah, thanks, Othniel, I've now read that. It seems to make a huge difference indeed whether you're playing Vanilla or Conquests. Main difference that in Vanilla you could still finish everything you were building, while in Conquests everything gets auto-switched to military, meaning you lose lots of shields that you had invested in expensive projects. And you can't even build artillery, if I understand correctly.
So, like Rysingsun says, it depends on what type of game you're playing. If you're not going for conquest or domination, you would probably only use it in an emergency. But if you have the tech, and it serves your win condition, yeah, why not use it?
In Vanilla you should probably use it every time, it almost seems exploitative, so strong it was there.
So, mister Capnvonbaron, don't get too used to this, cos otherwise you won't like the switch to Conquests!