Often enough. Setting up scenarios and RPing, mostly, as well as the odd bit of tidying things up(like rounding shipyard capacity to the nearest kiloton after continual expansion makes a mess of it).
Tho I used it more when learning, to correct beginner mistakes and derps, like the time I accidently deleted a battle fleet, or loaded all earth's mass drivers onto a freighter with mineral packets inbound("In breaking news, the Eastern Seaboard of the United States was obliterated in a tragic industrial accident last night! Yes, all of it. It's still early in the investigation, but inside sources suggest a typo in a shipping order was responsible.") - heh, after few incidents like that I used SM mode to transport my mass drivers around for a while.
I think the main use tho is 'simulated terraforming', where I'll note a planet's atmospheric composition, then use SM to fiddle with it, seeing how much of what I need to get the results I want and if it can be made habbitible at all, before using the aformentioned note to restore it to it's pre-fiddling condition, so I know what gas levels to use when terraforming it for real.