why wouldnt it?
if you raise the directed end of the antenna you are changing the angle
of radiation so you would effect the performance of the antenna
also effective if you live on a mountain top and want to work the valley
if you didnt lower the antenna it would shot right over there heads
you aim the antennas Az direction with good effect so why wouldnt
elevating the antenna has similar effect?

Caveat Lector wrote:
Had an experienced Ham claim that rotating an HF yagi in the elevation plane
would give significant signal gain on some signals.

Never heard of such a thing

Comments please