Yeah, no need at all. You don't want ANYTHING remaining from your last tank of water, since it could be infected.
One thing a guy could do is to set up the qt and do a water change on your display tank at the same time, then use the old display water for the qt tank.
Assuming your water is fine in your display, at least.
Although a guy might want to water it down a bit. Usually pet stores keep their fish @ 1.019 or so (in my experience) and your display is probably closer to 1.025, so if you bring it down a bit, then bring it up to your display over the course of a few days.
It's a method that makes sense to me, at least.
The other route is to QT it for a month and watch it for signs of anything.