I saw some champions being built with ardent censer, because well, it's really good right now. I played ivern and taric with ardent censer and the heals and shields were quite strong. I heard that someone also played nidalee ardent censer. What makes ardent so strong?
A lot of the currently popular ADCs are people like Kog'Maw, Twitch, Xayah, Tristana and Kalista. These are all pretty strong scaling autoattackers, so giving them an ardent in the early-mid game just makes them that much scarier. Ardent isn't as good on champions like Jhin and Miss Fortune, for example, because they don't autoattack as often.
Basically it's just overtuned. It just got another change this patch that removed the healing, but they also buffed the attack speed and made it apply to the caster as well, so I don't know if that's going to push it out of meta.
So mainly, it's for increased heals/shields/extra magic damage for your team.