Support Macro Tips?

I main Sona and Soraka in Silver, trying to get to gold. My winrate is above average on both, but I would like to up my game with some macro rather than just healing and supporting the team. What else should I do? How important is vision control? What role do I have in mid/late game? Should I roam at 15 minutes or so? What really difference do I really make? It's hard to judge how much you do since you can't compare damage dealt.
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