In practice, since the difference is so small it does not matter in almost all cases, because no one was in a position to measure accurately enough. If you ask for 100 feet of rope, the difference between the two definitions of "foot" is much tinier than the smallest possible roundoff error you or the sales person will make.
That's fine for measuring most things, but not necessarily for survey work. Your reference points can be quite far away, and you are dealing with angles. So ever pretty tiny changes can be significant.
