Where, when, and who are the three primary components of scene-setting in a script. For example:
''INT. WOLFRAM & HART - HALLWAY (where)- MORNING (when)
ON ILLYRIA (who)...''
Words like these in a script suggest to a director what is important about the scene, and — if the director agrees — help to cause the scene to be rendered in the way the author imagined it would have been.
Note that this might sometimes be where, when, and what, rather than who. An example from the same Angel script:
'' INT. RACQUETBALL COURT - EVENING
CLOSE ON a white wall for an instant...''
This helps the audience understand a change of scene by emphasizing the where of the scene. A quick visual transition to the who in the new setting is mandatory, unless the place is more interesting than the people.
Beseech the deity of your choice for mercy, O Writer, if the places are more important than the people.