Increasing your peak speed will help you perform better over longer distances.
Usually, when you go for a run, your primary goal is to keep your pace consistent for a considerable amount of time rather than to take quick, decisive strides. If you just run long distances, you only train your aerobic system, which burns oxygen to create energy, and your slow-twitch muscle fibers, which are built to resist exhaustion for extended periods.
To improve your ability to run long distances, you must develop your aerobic capacity and slow-twitch muscles, but sprinting may also benefit your training in other ways. If you solely trained your aerobic system and slow-twitch fibers, you could find it challenging to step up and rush to the finish when your natural urge to finish as quickly as possible comes in after a race.