Argument leverage is when a writer takes an argument that already exists and uses it as support for a new argument they're writing. In other words, they search for an argument and then add it to their outline.
Argument leverage is one of the most powerful features because the writer only needs to edit the point of the argument they are leveraging. The rest of that argument (its support and people who agree with it) then seamlessly become part of the writer's work.
TK: an illustration of a branch being leveraged and used by a writer in an argument they're working on.