Roof rails are for transporting stuff on your roof.
If you're not gonna use it - don't order it.
I ordered the rails on my VG GTS, but I am going to use them. I like how they look, so I guess unlike the trailer hitch there is a cosmetic component. But without that additional push from actually needing them, I don't see the point.
I have Dark Blue Metallic (which is dark enough that the side blades sort of disappear) and the black rails. I do use them occasionally, and I also like the looks. Some folks hate the rails and think they look stupid; others of us like 'em and think the car looks a bit "bald" without them. It really comes down to your personal preference. Either way, you're going to love driving your VG GTS!
While the question hasn't been asked quite a million times, a simple seach will yield you an interesting discussion.
I like them, ordered them and think any Macan looks better with them. One interesting point in the above discussion is that the rails will deflect rain from draining down over the doors, giving you an unexpected bath. Also, we're told they can't be retrofit.
If your reason for not getting them is that the Macan will then look more like a car...there are some great deals on remaining 2016 991's.