The advantage of monads is that they whisk away a bunch of boring, repetitive boilerplate code that nobody wants to write and that people will even go so far in other languages as to create a bunch of global/thread-local/hidden-context variables to avoid writing!

The downside is that the abstraction and its applications, maybe a bit like pointers, do take a while to really master. Particularly when you start composing monad types to make other monads, as Scotty does with IO.