Your audience will inform the purpose of your sketch, which ultimately will inform the type of sketching style or level of fidelity. For example, if we are in a brainstorm with our classmates or colleagues, the ideal sketch is loose and open to interpretation. It should capture the idea in a few gestural lines without much detail, that way your colleague can build on your original idea and make it even better. However, if your sketch is too tight, rigid and looks finished, then others won't feel as compelled to build on it.
"Dialogue with a Sketch" by Bill Buxton helps to illustrate a non-verbal conversation and
The speed at which we sketch can greatly influence the type of output or content we create. As a general rule, fast and sporadic sketch rhythm usually equates to more gestural output that stems from emotion and feelings. Whereas a slower sketch rhythm equates to more pragmatic output that stems from a cerebral approach. Either way, each sketch rhythm has its own superpower. For instance, the fast and loose style lends itself more towards form exploration and the slower and tighter style allows your brain to keep with the rhythm of the sketch, thus informing it and solving problems in real time.
Also known as "failing fast," is all about developing meaningful ideas by way of iterating through an abundance of throwaway ideas. Through this process, the sketch becomes merely a vehicle for thought. Remember, learning to sketch is only a skill, but sketching to learn is applying that skill to create something meaningful.