Unlike an editor who works on a publication from day to day and is hands-on, an editor-at-large contributes content on a semi-regular basis and has less of a say in matters such as layout, pictures or the publication's direction.
Editors-at-large are more independent; they are allowed their own preferences in the content they have to generate, and they do not always have to pitch their ideas to the main editor.
"At large" means the editor has no specific assignments, but rather works on whatever interests them.
The title of editor-at-large is offered as a way to keep the outgoing editor at the publication rather than lose his or her skills, connections and readership appeal, especially if the outgoing editor could be employed by a competing publication.
Such as André Leon Talley (died 2022) for Vogue, Diane WellPeth for Elle or Arnaud Henry Salas-Perez for Visionaire.