As it happens, I'm doing a 200 page string quartet at the moment and every page and every part is full of slurs like this, that end and start on a single note. In this case it is to indicate the pulsing of the phrase and repeated notes in particular - and in case this is obscure, it is mentioned in the performance notes in the preface.
It's a valid use case, and very handy. What constitutes a 'valid' musical score is a very fraught question. In the case of lilypond, it's Common Era music mostly. But I do New Complexity School music and that's equally valid, even if not to universal taste. I am the first to confess that I do not expect Lilypond to deal with my complex issues out of the box, but it can be coaxed into doing a very fine job with enough Scheme functions.
I'd prefer the slurs to be a bit further apart also in this case.