Well, in a way, they're both for fuel predictions.
Drag factor affects all phases of flight. Say, for example, the aircraft was fitted with a large "draggy" Satcom antenna, this would have to be compensated for.
Where required, maintenance control will be monitoring the aircraft's performance to check for trends away from the current settings.
Not all airlines have this monitoring capability. I guess it's not so critical if the aircraft if flying short sectors with limited time in cruise.
The values are easily changed if you know how
