Editors have to make sure that the writers' work fits their publications. This means guidelines for style, for accuracy, for acceptable grammar and syntax. The best editors take time to confer with writers about what needs reworking or clarification. The best will correct or eliminate serious errors, making both the publication and the writer look good. But when it comes to pressing deadlines, the biggest issue is to make sure that the content fits the allotted space.
Executive editors decide how much space to give to specific subjects like sports or the arts.
Department editors divide that space among their topics and give the writers estimates of how long their pieces should be. The writers try to tailor the significant facts and details to fit that presumed space. But by the time that stuff heads for the printer, the real space may have diminished for any number of reasons. In the theater the director is also an editor, cutting scenes or dialogue that don't fit the production. Maybe the director feels the intact play takes too long to hold audience attention.