I’m a big fan of sketching, and this post by Jacob Rader does a great job of explaining why it’s such an important part of the design process:

Sensemaking is the active conversation we have with the events that we encounter; it’s our ability to take in information, process it, and derive meaning and action from it.

Rather than focusing on the external, sketching provides us a sensemaking process for our own creative flux. When we’re presented with a problem our minds go to work to create this cloud of ideas, populating it with information and attempting to form connections. This facilitated sensemaking turns that abstract concoction into a concrete reality. This works because sketching forces us to make decisions and apply structure to our ideas. By externalizing we pass those fragments through a filter of our own experience creating a foundation to build our ideas from.

When we externalize the pieces of an idea through a sketch we’re making a testable “design move” which we’re able make judgements around. This positions us to make further moves that iteratively cycles and builds an idea.