It helps calculate the time for sleep or rest during long distance cycling and move with your custom average speed. Example: your minimal average speed is 15 km/h and your current average speed was 20 km/h over 10 hours then you will have 3.3 hours to rest. After that you should ride again to your average speed was at least 15 km/h
https://apps.garmin.com/en-US/apps/339f8385-33fb-4352-ae9e-6730cb3e48d5