Honestly, I've not done any benchmarking.

However, I would assume that if it is loading the route partials, it would add some kind of overhead. That being said, I would also argue that the overhead would be minimal.  Given the number of controllers that gitlab uses and its performance that i've experienced, any kind of overhead would be worth the added maintainability.

Also, I think that this would just be a valid point on a development environment. By default, if you were to change routes in production, you would have to restart the application to pick up the changes.