Using 500 mhz as minimum is more "productive" in terms of powersaving and avoiding wear on CPU (although, the second effect is probably very little). When You're using 500 mhz as min, Your CPU spend much more time @ 0 mhz during idle (every second, it's sitting ~2x longer at 0 mhz, after doing task @ 500 mhz), so you got additional benefit of saving on power leakage.

so, probably it's not about harm, but additional benefit It's also possible, that he doesn't have idea of power leakage etc, just like to have 500 mhz as starting point