Just because you don't have any lines does not mean you get a break while the other actor's lines are performing. Your reactions count more than the words that are coming out of your mouth. Remember...93% of language is about nonverbal communication (body language) as well as your facial expressions, and the other 7% are the words.

Same thing with editing...just because you have cut, clipped, teared, or marked any clips does not mean your job is complete. A good editor does not give up after the first full attempt of editing an entire Feature Film, TV Program or even a Short Film. There are so many elements involved with editing a film to include adjoining scenes and/or sequences, adding titles and music/scoring, rearranging clips and scenes, ADR (or looping), etc. Just like with essays, there usually is a first draft, second draft, third draft, and so on. Eventually with many drafts, the final draft will eventually come with hard effort and sheer dedication.