I only cast renew when I’m moving and literally all my instant cast heals are on cooldown. It’s been number 4 on my bars since Vanilla WoW though, so I don’t think I could relearn a different position for it on my bars at this point.
I use Renew to throw out atonement instantly when shield/rapture isn’t up or to help patch people up between packs myself. not something i go out of my way to use but i still use it enough to justify the keybind.
I keep PoM and PW:S on the tank on CD and have renew on all of the time during combat for the additional healing. I wasn’t using it a lot at the start of the expansion, but I leveled a resto druid and realized that a renew is almost as much healing as a rdruids base rejuv and germination together. So if someone gets about 10-15% down I may throw a renew instead of an casted or instant heal, if there isn’t anything too serious coming up. If they do become seriously hurt, they will also get bonus healing from renewed faith. In some cases, I will renew everyone in preparation for huge damage spikes like the Hyrja fight. 6% extra healing and a hot on everyone is quite a bit of help and might mean the difference between the squishy with 0% vers dying or living with a sliver of life if things go bad. As with every other holy priest spell, it depends on the situation.
I use Renew all the time, usually it’s for applying atonement when shield is on CD and can’t stand still to cast.
Renew doesn’t have the instant big heal like the other spells but it can still add up, there’s been lots of times where a few Renew ticks made the difference between life or death. It’s also the only heal that benefits from the atonement the spell applies so it’s really good if you have a decent amount of mastery.
Definitely want it on your bars and should be using it primarily for applying atonement more than the healing it provides.