One special category of pilots are those for whom going fast is important. Why? Because speed is relative. At altitude on a severe clear day, there's little sensation of speed. We have to get close to something before our speed becomes apparent. And the risk with getting close to something is we might hit it. While untrained pilots who engage in such risky behaviors aren't the norm, there's enough of them that the practice has its own term: unwarranted low flying. Its use apparently has fallen out of favor, but the phrase "unwarranted low flying" has populated numerous NTSB reports over the years.