If you haven't seen it recently in your work then the reason for making that recommendation probably does not apply.
A chart of ANSI pipe sizes clearly shows 5 Inch pipes in a full set of wall thicknesses, not something likely to happen if there was a reason to avoid it. Or maybe it was some very specialized application that is outside what your work entails, which is why you haven't seen it recently.
For example 4-1/2, 7, 9, and 11 inch are only listed in a small number of wall thicknesses; I would expect them to be not preferred.