"The roaming soldier functions as his team's offensive muscle class and acts as a backup pocket if the normal pocket dies. The roaming Soldier also functions as a suicide bomber, where the Soldier rocket jumps to the more important players of the team (Medic/Demoman) and tries to kill them early in a fight, or, in the Medic's case, tries to make them use their Ubercharge when they did not intend to. This job is usually relegated to a Soldier because of his ability to reposition himself with rocketjumps and take on the role of backup pocket. Some strategies might call for the roaming player to go for a specific strategic attack involving a class other than Soldier, like running a Pyro on Badlands."
DISCLAIMER: ALL AUDIO IN THIS VIDEO IS PROPERTY OF WARNER BROTHERS, TAKEN FROM "The Dark Knight Rises" TRAILER #3