Frances O Neill was thinking of the preservation of a body of music he feared in danger of getting lost. And so were, and are, other collectors. And that is just what he did.
His target audience consisted of traditional musicians who knew what was what. As a result loads of tunes went onto wide circulation that would otherwise have died out. Same can be said for the Breathnach collection, CRE has helped a vast body of tunes into wide circulation.

A great example is 'the Old Grey Goose', a six or so parter that O'Neil cobbled together by adding stray parts to a usual two paryer. It worked out great, Coleman recorded it and now we all play it the way O"Neill published it. That is what he was thinking.

It's certainly much easier to learn tunes by immersion but I can say I have lifted a fair amount of great tunes from several collections that I would not have encountered otherwise. And they have enriched my repertoire greatly.