I agree that sketching is an almost essential tool. You can sketch an idea on a napkin, on the back of your shopping list, anywhere. All you need is a pen and paper. You don’t need thousands of dollars worth of equipment and software to hone your skill. If you come up with a great idea when you are away from your computer, it doesn’t matter as long as you can draw. As designers, it is part of our job to communicate our ideas as clearly and efficiently as possible. I don’t care how fast you can model, I guarantee I can sketch way faster. Another aspect is that a persuasive sketch is one of the fastest ways to sell your design. As YO mentioned, excellent sketching is almost like magic to the lay person. If you are kick-ass at making sketch models or a 3D whiz, you can certainly get by with that alone, but why would you want to toss out one of the best tools you have?
There are very successful designers and architects that don’t sketch very well, so they must have developed effective work flows that don’t lean strongly on 2D problem solving. Here are a couple of examples.
This:
Became this:
Just from the sketch alone, would you have any idea that this:
Would become this?
In the above examples, if I you hadn’t seen either designer’s previous work, and they presented you with those sketches for their ideas, wouldn’t you (wrongly) assume that they were not very good? Drawing is a skill that everyone can improve with practice. I think it is well worth the time investment.