So far as I know, it's either off or on via a big red switch at the back. Can't tell you what current it draws when 'on' but not being driven, though. My guess is not too much (that's metric, not imperial measurements, by the way).
having had a look inside a couple of XLS200s I can say that they appeared to be properly constructed, having both a fused inlet and internal curcuit breaker, l'm pretty certain that it presents no greater risk than a fridge, tv, video or any other item you'd not think twice about leaving connected 24/7.
I expect that thread will alarm more people than it deserves to.
the chances of your XLS200 causing a fire are very small. especially compared to TVs, which universally (AFAIK) use what I would call 'cheap & nasty switched mode technology' which is IMO seriously less relaible and safe than a properly constructed conventional (transformer + bridge recifier) power supply.
but obviously you can't be any safer than if the power is disconnected from any unused appliances, an unpowered item is very unlikely to cause a fire.