I second everything that YO said and will add my two cents.
Not only is sketching important, but sketching WELL is important. In my experience potential employers and clients are looking for someone who not only understands manufacturing and 3D modeling, but sketches like a mad fool. I have actually been passed up for jobs because I couldn’t sketch as well as the employer would have liked. If I had any advice to give to anyone, it would be to sketch as much as you breathe, it, like breathing, can only help you. I am regretting now not putting as much time as my classmates in school to improve my sketching and my career is suffering as a result 
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Sketch on!