I have had at least one incident of ruining a recording session when the vocalist took a deep breath just before belting out his tune, and getting such a nose and mouthful of dust out of the mic (that had been left on stand and open for a few days) that the session was effectively over for the day.
Since then, I sometimes do leave mics on their stand, but slip a small plastic bag over them when not in use. The bags also have a small silica gel sachet taped to the inside, just as a (probably needless) precaution.
I usually unplug the mic cable at the pre-amp side - not because I am afraid of anything nasty happening electrically, but because when my German Shepherds rip through the room, they tend to get entangled in the cables and seem to enjoy dragging everything along with them.
Therefore, I unplug the cable at the pre-amp side, loop is up and hang it high from the mic stand.
Friends have advised me to route the cables from the ceiling, which probably makes sense, but seems too much trouble to me right now.
BTW - I have an ionizer on in the room 24x7, but that has something to do with my sinuses, and less with the equipment. Now that I think about it - could this cause some kind of problem with equipment?
I'm cringing at the thought of German Sheperds running through a studio!
So I can let her run in the "studio" without worrying about having to fish mic cable out of her ass.