As long as you use good quality outer of a decent length, there's no real need for a rollamajig, even for chainstay routing. The only advantage is if you feel a need to run a very short outer to avoid any chance of the cable getting snagged on trail obstacles - even a good quality outer will deform and constrict the cable inside it if you make it take an extremely tight turn. But provided the outer is on a curve of a decent size that doesn't deform it, the cable will run perfectly smoothly without a roller device.