Joe I am well aware of what the original question is/was. You yourself also commented on the practicality of one sheet vs two. I was simply asking more information on comments by other posters, including yourself.
Okay.. here's your question:
If your headsail is on a furler, what does using a bowline over a cow hitch provide?
I'll try... but it's apples and oranges... because you can't cow hitch a two line system, and you can't bowline a single line system. However, if you have a choice... let's say you're buying a new set of sheets... the two sheet system will allow you to rotate end for end, switch sides, or simply stow out of the weather when the boat is down... That means your can extend the life of these valuable items indefinitely.
The single line system will allow you to use the flatter, cow hitch... giving one the perceived advantage that it improves tacking. It is very common for boat owners to NEVER remove their sheets when their boat is rigged this way. So.. the sheets are changed out more often than the two sheet system (increasing cost) or the sheets remain unchanged, deteriorating in the elements.
There are other ways.... you could install a lightweight, hi tech pigtail to which you would attach your single or double line sheets, putting them some distance from the clew. On my Nacra the pigtail is a length of 1/4" Samson XLS light that is doubled and
COW HITCHED through the clew. It is left on the jib. The sheets have a small block at their ends that allow it to be doubled back to a becket on the lead block/cleat device. The pigtail is bow lined to this sheet block when rigging the boat. It gives the jib sheet a 2:1 purchase.
I guess all my jibber-jabber about this is to show people that there are many ways to develop an efficient sail handling system. Some people buy their boat and simply accept that the way the previous owner had it set up was the "Right" way.... and I just want to show them that there are acceptable, even preferable, alternatives.