Many of us have a slight hearing loss in one ear.Anyone in that boat correlate the difference with the ear exposed to many years of road noise and wind, i.e., the LHS - or RHS for brits? I have suspected for some time this could be the reason for mild HF loss in one ear, possibly exacerbated by the same side being preferred for cell phone use. Another cause for some is probably from shooting guns since hearing protection years ago was not as prevalent as it is today.
My SMc preamp has two or three notches of mild balance correction on each side of the center detent. I rarely use it but it is nice to have for a few recordings that are noticeably out of wack. I do not notice any loss of fidelity when it is correcting balance but my speakers are positioned for optimal balance from my typical chair and even though the effect of the control is mild, I rarely go beyond one notch over. I could probably live without it, and did with most of the 20-some preamps I owned before settling down with the excellent SMc unit.