Result.m vs. with-syntax

Hi @skirino, 

Pardon me for bothering you again, I am trying to make sense of `Result.m`.
In our current gear and antikythera code, `Result.m` is often used over standard library's `with` syntax, and the result is usually wrapped in `Result.pure` instead of a simple OK tuple. 
What are some of the benefits of using `Result.m`? and what are some of the tradeoff made?

Thank you!