Defining the scenario is linked to the criteria but removes the constant constraint. This allows you to define more complex cases where all metrics can vary at the same time.
A common example is to make the user (client) number a variable moving with the time: the response time will be constant from 5 users to 1,000 users with an increment of 5 users every 10 seconds.
A scenario is generally very close to the actual application usage but also harder to work on if you don't encounter it immediately because you are no longer running the application under a constant load. This is why they are seen more as validation checkpoints than work criteria.
