On a documentary production, or an improvised fiction film, the editor is really the second director, since the materials supplied are usually capable of broad interpretation. Putting it more crudely, they are inherently entertaining but lack design. Unlike a scripted production, editing requires that the editor often make responsible subjective judgments. But even in a tightly scripted fiction film the editor needs the insight and confidence to know when to bend the original intentions to better serve the film's underlying goals. Editing is always far more than following a script, just as music is much more than playing the right notes.
Composing is in fact the closest analogy to the editor's work.
With low-budget films, however, economics may prevent cutting until everything is shot. This is risky because errors and omissions surface when it is too late to rectify them. One should therefore try to arrange to see dailies. Shooting on video allows rushes to be viewed immediately, so that any reshooting can be scheduled before quitting the location. Many 35mm feature film cameras now make a simultaneous video recording, which allows instant replay and mitigates the unit's absolute dependency upon the script supervisor's powers of observation.