“Related Items” is almost useful
I use Related Items pretty much exclusively for “This paper references that paper” or the like. But relations have no directionality, so there’s no way to tell, without opening the paper and digging through the references, which one references which. I’d like “types” of relations, where we can click on a widget and maybe cycle through different possibilities.
https://github.com/MuiseDestiny/zotero-reference
https://github.com/MuiseDestiny/zotero-reference/issues/305
With that sort of functionality, the Related tab becomes less relevant. It has always been inherently somewhat ambiguous. The entries one adds might be mainly cited papers, but can be varied - important cited works, other works by the same authors, other related works, etc. With no way to signify why you added each item.
At some point I would expect the Reference plugin-like citation functionality to be added to stock Zotero, such is the importance of citation tracking (and the increasing ways for Zotero to do it, from online repositories). At that point the Related tab could be more clearly defined as just for non-cited/non-citing papers.