It depends on what do you want to do with the session. So it's up to the one that is defining the architecture to decide if to use one or more sessions. It depends on the data and what you want to do. You mention that you are in an ESB, but what kind of data do you want to handle, what kind of processes and rules do you want to run, for do exactly what? these questions needs to be answered in order to decide.
Cheers