He's correct: for the spats to look neat and proper they need to fit snugly. Loose spats look sloppy.

It's one of the many reasons that civilian bands who decide to go with Full Dress (doublets, feather bonnets, horsehair sporrans, spats, etc) often don't look as smart as bands wearing the normal modern civilian pipe band dress (Argyll jackets, ghillies, etc) : there's less to go wrong with the modern dress, and precise fit is not as crucial. Anyone can throw on an Argyll jacket and look OK but a doublet must be tailored to fit, and anyone can put on hose and ghillies but spats must be fitted exactly.