"if it fits and feels right" does not always work either. I've seen some set ups where the person looks and must be very uncomfortable and well as inefficient but they say "it feels great". If I'm not asked for my input I do not offer it.
It is often because the person has become used to/adjusted to the fit rather than real comfort.

Handlebars fit has a fair degree of fit tolerance within reason. Too wide and control can become a problem as well as rotating the wrists too far inward when in the drops...on a rode bike...and probably the elbows locked and shoulders stiff. Too narrow and the chest can be compressed a bit possibly resulting in breathing being a bit more laborious than necessary.

Also the type of road bar makes a difference in addition to the size. A deeper drop, etc. on same width bars will feel differently.