I'm a big fan of sketching ideas and consider it to be a key design skill. One of its many benefits is that stakeholders and project managers and salespeople are comfortable recommending changes. The know that it is "nothing but a sketch." However many people I speak to say "never show a sketch to a client" and, I have to admidt, that many times I think they are correct; especially when the stakeholder says "why are you showing me sketches?"
Stakeholders often times feel that they are wasting their time looking at sketches and don't particular warm up to the idea that making more "presentable" representations take time (hence money). They like the idea of not wasting money but they feel that it is the designer who should "waste his time" making things presentable as opposed to them "wasting their time" reviewing sketches. Too many stakeholders do not understand the value of a sketch. The question, I suppose, is "how do we change this perception?"
Another benefit of a sketch is that it helps to put a form, a face if you will, to the idea that's floating around the room. We all may be talking about the same thing but the image we each have is different (sometimes very, very different). Sketching out the concept allows us to be focusing upon the same idea AND often times generate multiple leads from what was originally thought to be one idea.
And yet another value of sketching its that it functions as a recording of design ideas. It's a story board of when the idea(s) were formed and often are themselves the springboard to new ideas.