One of the common complaints I see about S8 is the amount of unresolved/dropped plotlines. I never noticed this though and I feel it's a bit hyperbolic.

The entity is one example that I often see cited. Allura never had to experience the awful consequences of it (though the headaches screwed over Team Voltron at one point) but it was an important moment for her to show how far she was willing to go to stop Honerva. And I do think it absolutely factored into her decision to sacrifice herself at the end since she was doomed otherwise anyway. It might've not been the most satisfying resolution that could've happened, but the entity was still important enough to the story that I'm surprised people are writing it off as irrelevant.

Anyway that's just the top of my head. I'm sure there's a ton of stuff I missed.