What are real advantages of brake hose junction connectors?
For your own bike, you would probably only do that one time, when the bike is new (to you) and setup opposite to your preference. 

The big advantage in this situation is that you shouldn’t have to unwrap that lovely fresh bar tape to do the job, and you are undoing specially designed connectors, instead of the compression fittings at the lever. There’s less to go wrong, certainly no need to fit new fittings or shorten the hose for them, just a couple of spanners are required. More lay-user friendly. 

Otherwise, If you had a rental fleet and foreign customers, you could swap the hoses around if any customer requests it, then back again. I assume; I don’t know how many swaps the connectors could handle, but it would be preferable to swapping at the lever end. (Quicker, easier, no need to shorten the hose for new compression fittings).