Every support main should play the other roles at least once in a while.

Why? Because helping your team is your job as a support but you can't do that effectively if you don't understand what your team needs. You also can't effectively shut down the enemy if you aren't familiar with what they're capable of. I main mid, jungle, and top, but I also play support fairly often to very good success, and I attribute that success to knowledge I've gained from my 3 main roles. I see so many supports that focus way too many of their resources on a single threat while allowing other threats to run rampant. I see way too many supports who babysit their adc who doesn't need the help while their frontline gets torn to pieces. And I see way too many supports who cannot accurately gauge threat levels of specific enemies because they have no idea how much gold and exp is actually worth since they're so divorced from either. It's not a coincidence that Aphro, a converted adc, is widely considered the best support in NA; he knows exactly what his team needs because he's been there.