"If you can't explain it simply, you don't understand it well enough."
- Albert Einstein
While quick drawings are the most effective tool in the early stages of exploring ideas, you need to capture your solutions in more detail. You can capture a more detailed design solution in a schematic way with wireframes or in a more realistic way with mockups. Each technique is adequate to cover specific objectives, and you may prefer one or the other depending on the type of your problem.
Some teams will find no benefit in creating detailed wireframes from sketches. They feel comfortable discussing ideas as sketches and move directly to produce mockups. Other teams may use wireframes to focus on functionality and behavior in great detail, leaving the graphical visual aspects for a later stage. Being familiar with both tools...