While going around to some thrift stores today, I came across several otherwise nice ties (at more than one store) that were permanently mangled in two spots -- one on the wide blade, and one on the narrow -- where the knots obviously were. Well, I assume the mangling was permanent; I had no desire to so much as attempt the ironing that would be required to even try to remove the appallingly deep wrinkles, so I didn't even consider buying them.
I strongly suspect this mangling was the result of the previous owners keeping the ties permanently tied, where they just loosened the tie enough to remove it from their necks, then stored the ties still knotted.
That's why you should never, ever do that; over time, it will permanently ruin your ties.
But, you may ask, what's the difference -- if the wrinkles are in the knot anyway, who's going to see them?
The difference is that the same tie may need to be tied differently with different clothes. With trousers of different rises, the same tie may need to be wrapped once instead of twice (or vice-versa), or it may need to be started higher or lower on the chest. And a wide, spread collar may require a Half- or Full-Windsor knot, instead of a four-in-hand, to adequately fill in the gap between the collar.
And, even leaving all of that aside, any man who cares about his clothes should not want to ruin his ties just for the sake of not ruining them, even if he really is ruining them in a way that only he can see.
Some experts even advise untying your tie by reversing the steps of knotting it, instead of just pulling the small blade through the knot's hole, so the knot automatically falls apart. It certainly doesn't hurt to do that, but it's probably going too far in the other direction, to the point of being too careful; I've never once done that, and I can't recall ever having a problem with the wrinkles from the knot disappearing on their own by the next day. But it's still best to pull the small blade through the knot and to untie your tie as gently as possible.
Your ties should only be tied when you're wearing them; always store them untied.