Stopping exactly on the far lip is required in order to properly reverse to the new layer
But unless the error was such that you had accumulated an integral number of wire thicknesses, that's not going to help.
Let's say it nominally holds 100 turns along the length. You measure that the wire is a bit thicker say, and by the time you get to where the 99th row would be, you think Oops, we've actually got 99.5 thicknesses. So what do you do? You can't fit another full turn into 0.5 of turn's gap, so you can't stop exactly on the far lip anyway... not in terms of wire widths.... so you reverse with half a wire width gap.
(That made sense to me in my head- might need a drawing to describe it but I cba doing that right now.)
Point is, I'm pretty sure there are best-practices for doing this commercially, and I don't think this is one of them with all due respect.