Saves money during production. Repetition and echoes can be used to tag secondary characters. Dangerous technique to use with leads. In a good screenplay, there are lots of two-inch scenes. Sequences build pace.
Small details add reality.
Don't number the scenes of a selling script. Action and humor should emanate from the characters, and not just thrown in for the sake of a laugh. Comedy which violates the integrity of the characters or oversteps the reality-world of the film may get a laugh, but it will ultimately unravel the picture. Don't break the fourth wall, no matter how tempting. A character's entrance should be indicative of the character's traits.