Early game, you'll probably follow only your carry. You may leave him in some circumstances:
- Warding river / red / blue to keep track of junglers (prevents ganks and allow counter jungle)
- One of the enemy botlane switch to another lane, you MUST follow and let your carry take care of the lane (if he can't 1v1, he's a bad carry). Some times though, it may be more effective to stay here to deny farms and let your carry fill/create a gap. But be sure other lanes are doing fine and won't be impeded by one or more champion in the lane (bot + jungler)
Do not leave him if a champion is dominating at this moment. Keep an eye on when the enemy begins to team up. Before that point, your carry may be able to invert the steam and come back in the game. But he won't do it alone.
In mid game, you have to support the "real" carry of the game. Don't waste your energy on a bot AD carry that is 0/8/2 when you have a 10/2/22 top. He is the one who must stay alive (worth much gold, high damage burst, high disruptive power allowing team to score, ...). If the intended carry (a.k.a. bot champion) did not get enough farm/kills, forget about him. He must try to fill in the gap as he can, with farms on incoming creeps or so.
In late game, you have to be were there is a team. You won't be efficient if you're going duo with an AD carry (unless maybe if he's hard fed). Your auras should benefit the maximum of champions.