Clary sage is a distinct plant from culinary sage and a far gentler oil. Its reputation rests on two things: it is genuinely antispasmodic, meaning it settles involuntary muscle contraction, and it is calming to the nervous system in a way few oils match.
For feet the first property is the practical one. Night cramps in the arch or the toes are involuntary muscle spasm, and clary sage acts on the spasm rather than masking the pain of it. The calming effect helps for the obvious reason that cramp usually strikes when you are trying to sleep.
It is also mildly antifungal and a decent deodoriser, though those are secondary reasons to keep it.
