not really worth the effort for most people, but I'm a collector and completionist and I'd like to eventually get most everything (non-DM) at least MLB or BLB. I'm one of the crazy few that BLB all 4 holy beasts plus huanglongdong too
Plus for general farming I always rotate through unique ones that I like, for example using a farming team of all wargreymons or garurumon variants. Not always the fastest but I enjoy it more. Same for mono events, I cycle different mons through each time to change things up.
This is probably part of the reason I'm still enjoying this after almost 1.5 years playing and expect to be around for a long time