With the amount of fish disease parasites out there. It is worth it to qt regardless of where/when you get a fish. I never did until I got burned. Lost every fish I owned. A 20 gallon bb tank with pvc heater and powerhead are is all you really need.
That's what usually happens. Get burned once or twice and qt doesn't seem like such a pain in the butt anymore.
To me it's one of the great mysteries in this hobby. Some ppl never qt and get lucky again and again for years without ever getting disease. While others who appear to provide the same diet, husbandry etc, who don't qt one fish and wipe out their tank.