Suggestions

I think the origins are well lost in history.  It's Irish but very commonly used in Scotland (obviously there's been a bit of traffic between the two countries), and it's a bardic form.  The sonics are vitally important -- the bards used sounds to build moods and rhymes would aid memory, since connachlonns (like most bardic forms) could be very, very long.  They're used for ballads, mostly, and can be quite heroic.  Essentially they're poems about people/gods/heroes.