Why use Trace to test branch logic instead of Run?
Why ask a basic question in a forum instead of trying Trace and Run in Developer to see the difference? 
Trace will mark each step executed so you can see that the correct path is taken.
Run simply executes the service from start to finish on the server. When finished, the end pipeline is shown in Developer with no indicators of the path(s) taken.
Please review the Developer’s user guide it should explain the debugging flows methods:)