Here is a instance where the Horizon Shift would have been promptly advantageous. here I would like to have sand reflections, but not just specular highlights in the form of dots, but also a spread field of ambient definition. However, when using roughness for the specular highlight dots, this changes the horizon shift as you explained, while the ambient specular has no horizon shift, and thus they do not match up and have a visible offset. Changing the ambient with a constant or PF changes my desired look and isn't a fix. An unfortunate realism-killer.