The ability to pull in segments of other pages into the current page. If you change it in one place, other references will change.
I'm still a little hazy on usage, but seems to be useful for building up arguments/articles built from various thoughts, without having having to have a full page for each of those separate thoughts.
I am dabbling in the Zettelkasten method, with using Org-roam. I keep my notes in a repository where my network of notes reside (I guess people call them evergreen, concept, or permanent notes).
When I start writing something long-form, I want to have a writing project separately from my notes repository, assemble relevant notes to form a basis of the long-form material, and avoid having multiple copies of notes flying around.
Transclusion should let me do this.
2 Reference vs embed
A block reference is one way, in the sense that it is a copy that links back to the original instance and is dependent on it. What I mean is, if you edit the original, the reference will change to, but not vice versa.
On the other hand, all block embeds of an original instance are related and interactive. Edit any one of them, and ALL instances change.