robot_state_publisher, for gazebo only or for actual robot?

Hi all The robot_state_publisher publishes transform (which is usually based on the URDF file specified). But when we are talking about the URDF file, we are usually talking about Gazebo, which is for simulation. Ok. But if I want to do ACTUAL physical robot, do I still need to use robot_state_publisher to publishes transform? I am confused. If robot_state_publisher still publishes transform, what happen to the PHYSICAL base driver of the robot? From what I know, the base driver publishes odometry and transform as well. I am very confused.