Basing it off of [1], nothing is lost from traditional notation, inasmuch as it's extra notation on top of traditional notation. In this sense, it's a bit similar to furigana[2] for Japanese, as an aid to readers. Something that surprised me is that [1] is of a minor key, but the solfege marks are for the relative major. I'm not a singer, so I can't say as to how/why that makes sense.
1: https://en.wikipedia.org/wiki/Sacred_Harp#/media/File:Windha...
2: https://en.wikipedia.org/wiki/Furigana