When you write a script using the New Window script step with the Using Layout option in FM 16 you will not only create a new window but also end up in the right layout / table.
If you use this script in FM 15 it will stay in the original table, because the Using Layout option is not supported in 15.
FM does not throw an error of course but does not give any compatibility warnings either.
Depending on what happens next in your script things can go horribly wrong.
Adding an extra Go to Layout solves the problem and creates backward compatibility.