The strength of sketching is that it’s a fast way to capture ideas.
Since a low-fidelity sketch is fast—pen on paper, as shown—it’s also low cost. And low cost means it’s relatively disposable if it turns out you can’t use that idea.
If you don’t like my first 5 ideas, that’s OK. I can have more ideas, easily and at low cost. And so can you.
A variation on this theme: iteration is also painless. With relatively little invested in a sketch, modifying an idea costs marginally more.
The payoff is that you can quickly saturate the problem space with ideas, before you analyse them. This is a key part of why Five Sketches™ works so well for development teams who are in a hurry to start programming.
It’s important to keep sketches cheap. Here’s a video of a cool sketching tool that, if used as a design aid, would greatly increase the project risk. That’s because this cool tool is expensive to install, expensive to learn (it requires training) and expensive to use (it allows only 1 user at a time). All this will reduce the number of sketches in the problem space—and it’s risky to design without considering all options.