If you live in an area of high humidity, leaving it out on a stand is not going to do the guitar any permanent damage whatsoever.
Two things will happen. First of all the action will become stiffer because the domed soundboard will swell slightly as it absorbs moisture, thus raising the level of the bridge ralative to the fretboard.(Actually it is the soundboard bracing that swells, but lets not get technical) Secondly, the quality of the tone will deteriorate slightly, as guitars always sound better in a dry(ish) environment. Humid conditions make them sound slightly flabbier. Neither of these pronlems is permanent , serious or irreversible.
HOWEVER, if you live in an area of low humidity, like New Mexico or Arizona, get it back in the case immediately. The best case scenario is that the lacquer finish will start to craze and crack, worst case is that splits will develop in the soundboard, sides or back. Keep it in the case with a Humitor.
Or emigrate to Britain. They dont have the same humidity problems there!