hot days and the defroster

[erc84]

I have a 1995 3.8 V6, on hot days sitting at long stop lights or stuck in traffic, in other words sitting idle for a long time, I turn on my defroster on high, to relieve some heat on the engine. Is this a bad thing to do?
In my mind what I think happens is that the defroster just takes some heat from the engine and gets it out through the vents inside the car or is that false? Or is what I do at those stop lights/etc OK to do? I don't leave the defroster running while driving, just at long stops.
Overall is that OK?
Thanks