How useful is the formal definition of the second, really?

Oh, great! That means I have to reset my watch again in 300 million years! Thank for nothing!

Every now and then they have leap seconds. :smiley:

Understand, the second itself is the same duration, they just skip ahead or back one.

My background is not in physics (nowhere close) but I would assume that you look at the behavior as it gets close to 0 K, and extrapolate the limit.