Serenity Chakra state is more situational in raids. In general, you don't need it, but there are some fights where it makes a good candidate. For example, if you are healing the kiter on magmaw HC; then all you really need is potent single target heals (and body & soul). Serenity chakra is good at these situations. A holypriest is never excellent at single target healing, but unlike WoTLK, we can actually do it these days. It's just a little waste of potential to do so.
The major benefit from the serenity chakra is actually the serenity spell. It's a brilliant, cheap heal. I find that if I overextend myself on the mana situation, simply switching to serenity and spamming heal + serenity, I can handle both tank and raid healing moderately well, while using virtually no mana. I will be underperforming while doing so, and the HPS will be pathetic, but do not underestimate the life-saving powers of an instant single target heal. It's basically why I pick Desperate Prayer too