The last few seasons have featured an end-of-season collection event - so far we’ve seen shards, medals, coins and rings. The ring collection event was cancelled due to a bug, but may reappear this season as it may have been fixed in the 1.16 update. Or LightHeart might have something different in store - equipment? upgrade material? XP?
As BP rewards (free and paid) count towards the event, defer collecting them (except of course the bonuses like I’ve done) unless you really need to - for example if collecting the shards will star up a hero you play with, or medals help you promote a playing hero (or unlock an all hero bonus you are working on), then it’s not worth deferring that.