Is there any advantage? The only one I can think of is if you wanted to carry the bike on your shoulder, but apart from that....?
That's about it - it mattered more before trail centres!
No advantage whatsoever. In fact, I reckon it worse becasue the cables scratch the frame and that's THE worst place becasue you can see it. I also sit on my top tube when we have a breather, which makes it worse.
Full outer cable now means that most manufacturers put it under the tube as it looks cleaner... before it was at the top as to keep the exposed inner cable away from dirt and grime.
no real advantage other than what you pointed out in your post
However, running the cables along the top tube(under or over) and down the chainstay gives you a better line for the rear mech,and rear brake. (IMO - :wink:)
My preference when building is side of the top tube - on top or underneath means the cable has to curve around the head tube and seat tube. With a Rohloff build especially, the left side is very neat.
Over works if you've got V-brakes or Canti's, under would put a big kink in the cable arround the seattube and back up. I prefer over as I still like to pick my bike up to throw it over stiles or cary it up a hill on my back, etc.
Thanks for the insights.
I hadn't thought about the dirt aspect, though I wonder if the underside of the top tube ever really gets pelted anyway.
I conclude my preferred arrangement is full outers routed under the top tube!