This feature if a way of "keeping an eye" on predictions in the notification are so you can continue to do other things on your phone.
When activated this will put a numbered icon in the status bar with an ongoing notification.
When minimized, this icon will have a number overlay that represents the number of minutes until the next vehicle is set to arrive at the watched stop.
This provides a quick and easy way to keep track of arriving vehicles while you do other things on your phone.
Expand the status area to view the more detailed ongoing notification for the watched Trek.
When expanded, the notification shows the name of stop being watched and an abbreviated, comma-separated list of route predictions in the format of ROUTE : TIME.
This provides a quick and easy way to see all arriving routes at the given stop without having to open up the app.
Click on the notification to open the Actions dialog that will let you act on the Trek being watched.
The route predictions will automatically refresh every minute on the minute, so they're always up-to-date based on the last notification time.
However, if loading route predictions fail for any reason, an error message is displayed with the last known refresh time instead of the stop name.
The notification time (in the lower right) continues to indicate the last time the notification was updated.