Clocks used to be able to use the 60Hz cycle to track time, and grid providers would run slightly slow or fast ("time error correction") to get back into sync. A leap second would just be part of this.
I believe in the US this error correction has been discontinued in the East and in Texas, but is still done in the West for some kind of non-clock "inadvertent interchange" reasons I don't understand.
Wait is that why my oven and microwave clocks are constantly getting out of sync by multiple minutes every year?
Out of sync with each other, or are they drifting together in lockstep? In the latter case, yes, that's the most likely explanation.