Yes, I know what you mean; I did find however that if you power 5V logic from the same supply you can get brownout type glitches because the 5V rail can bounce and sag if you connect and disconnect a large load on the 12V rail.
I found that doesnt happen (as much) if the resister load is pulling a couple of amps.
It may just be my dodgy skip salvage PSUs tho...
Jim