Where you have the gain set has nothing to do with whether or not you're
A)
abusing it, or B) overdriving it.

Half gain may be WELL into clipping
depending on the output voltage of your HU, which can, over time, hurt
your
amp. Just because your

Care to explain how this can hurt your amp ?

Overdriving an amp can be harmful due to excess heat. Most amps hold up
reasonably well though.