The most difficult part of any design process can be finding the correct, best, or most successful idea out of all possible ideas out there. In User Experience (UX) we start by finding empathy with the user, researching user preferences, successes and failures, and understanding the needs of the clients. However, even armed with research and understanding, discovering or uncovering the correct solution out of all the possible solutions out in the world can still be problematic. Used appropriately, sketching is a fantastic way to generate new ideas without the usual constraints we put on ourselves with technology.
Sketching is a simple, inexpensive way to find solutions and weed-out errors.