Ok, so using the exo as an example, using a bender will allow you to do everything you need to do to make the exo-cage. No, you won't be able to make big sweeping arches, but the same area can be protected just the same with a couple light bends and some straight tube. Now if you only had a roller, you would not be able to do everything to make the exo-cage. There will inevitably be some tight bend that will need to be done that a roller simply can't do. Unless of course, you are doing an exo on the above mentioned VW or something from the 1930s.
In addition, a guy I talked to that did a lot of motorcycle frames back during the whole "chopper" craze called the roller "a tubing waster". According to him, it takes a long time to get used to using the roller in order to make two or more duplicate bends and he said it developed a lot of scrap since the tube being rolled usually needed to be longer than the actual part in order to feed it through the rollers. I've never used one myself, but he seemed pretty experienced with it so I took it at face value.
If I were setting up a new fab shop, a tubing bender would be one of my first purchases right alongside a welder. A tubing roller would be one of the last and then only if I had the extra money, space and a specific job lined up to use it. A bender is a typical tool used in almost any chassis or cage build, a roller is a specialty tool used only in a few specific instances.
