The patent is titled "Method and Apparatus for Automatically Adjusting the Operation of Notifications Based on Changes in a Physical Activity Level." No, it’s not exactly the most subtle title in the world.
Basically, the system would be able to detect a change in physical activity and switch settings as a result. Perhaps you have Do Not Disturb enabled when you’re exercising or you switch to airplane mode to conserve power.
You may worry that the system might trigger if you have to run for the bus or chase after a straying child, but Apple is one step ahead of you. The filing states that "a short burst of activity - e.g., running to catch a bus - is not mistaken for the beginning of an exercise workout."
It seems like a useful system if you don’t want to manually switch settings before and after your workout, and saves you the hassle if you forget.