Whether or not you "subscribe" to the use of deliverables in UX design depends a lot on the methodology you practice as a designer. Where one designer might find it useful, or even mandatory, to produce a deliverable for every stage of the design process, another designer might work within a team that lives and breathes Agile.
Being able to visualize a concrete solution to your problem is at the heart of design, (Goodwin, 2009). Solutions themselves range from finished, tangible products (such as a building or a new piece of technology), or they could be products that provide an "experience" to the user.
There is the danger of the UX designer focusing too much on their deliverables - and becoming disengaged from the larger project as a whole. Diagrams are great when they contribute to the production of the website, diagrams for the sake of making a diagram does nothing to help the ultimate goal. If the document does not contribute to the project, team, or final product, the document has been utilized inappropriately.
Kim Goodwin, "Designing for the Digital Age," (2009).