If your team is aggressing, your job is to jump forwards and get their team to look away from your combo without dying.
If their team is aggressing, your job is to sit near your medic and help kill the things that fight your combo (usually bombing soldiers)
gunboats is a thing to be able to take space more effectively, that's why some soldiers will run banner on last holds because there's not much space to be taken unless teams go down 2+ people (rare when the team on last has offclasses)