This boat belongs to a friend of mine. He does indeed use the barber hauler for a smaller headsail he sometimes sets, helps him close the chute with the main and point higher for races.
As soon as I saw the boat name i realised it was the boat you mentioned in the other thread and that they wear colourful shirts
When I was thinking about the race sails etc, I was thinking that for a small sail I could fit a jib track on the cabin top which would also require me using the winches up there, so I like that solution.
That additional smaller track is exactly what the SF37 has and I use that track for my 105% headsail. I have also seen another SF37 that also had barber haulers for there large no.1. They said that although as you point out the side stays limit the amount the mid girth of the headsail can come in, by using the BH they managed to pull the clew in enough that it made the chute slightly smaller and more efficient for them, again just for racing. Only problem with the cabin top No.3 tracks is that when you bear away to a reach the sheeting angle is horrible and produces a bucket shape in the headsail, just like you typically see on self tackers. My solution is that I run paired jib sheets through both tracks so that when cracked off I sheet through the outboard tracks to produce a better sail shape.
I will say that using the top tracks (and the cabin top winches) is a joy going to windward, tacking only requires the most minimal sheeting, perhaps only one metre of jib sheet to take in or release.