Honestly, you can use Renew as much as you want if you're not going OOM. These 101 guides are my advice, but everyone has a different playstyle and if you can kill dragons with it, then have at it.

As a player I value efficiency over most things and Renew is a utility for me because it's inefficient. If a target is taking an unmanageable amount of damage, I use Renew. But most DPS who take a little bit of random damage do not take more damage and I don't find it necessary to put a Renew on them. Renew means you can drop it on someone, they get some heal, and then if they need more you get back to them later. But if you just get back to them later without the Renew, more often than not their health hasn't budged since they took damage the last time. People have to break the habit of trying to get everyone in the party up to full as fast as possible. It's not necessary to top them off.

Only when a target is taking direct damage or expecting to take direct damage in the next 5 or seconds do I put shields and renews on them. If they're standing in something, heal them, if they're a tank heal them. If it's a DPS who just took a couple ticks of a whirlwind before moving, I can find the time to get back to them with a Heal at my leisure.