Speeding up
Scenario:
Long haul flight, many pax with onward connections at the far end, and you have a delayed start.
Are you able to "put the foot down a bit" to try and make up time?
Pro- you get to the destination having made up time, hence less pax are affected (which in turn may mean less costs to the airline having to deal with the dealys eg. re-booking, hotels, etc.
Con- More fuel burn, more stress on the engine and airframe, etc