The docs for this option say "Whether to make use of extra commas in import/export lists (as opposed to Ormolu's style)", but Ormolu uses trailing commas on multi-line import and export lists (and I'm pretty sure it has since before fourmolu was forked), which would seem to be the "diff friendly" style.

In #19, tweag/ormolu#409 is referenced, but that issue isn't about commas, but rather the position of the parens.

So, I guess I'm asking for that documentation to be more explicit about how that option actually affects the formatting.