Description
File entity provides interfaces for managing files. It also extends the core file entity, allowing files to be fieldable, grouped into types, viewed (using display modes) and formatted using field formatted.
vs
Media entity provides a 'base' entity for media. This is a very basic entity
which can reference to all kinds of media-objects (local files, YouTube
videos, Tweets, Instagram photos, ...). Media entity provides a relation between
Drupal and the media resource.
From those 2 descriptions from file_entity module and media_entity module, I may be hard for a site builder to decide whether to use a Fieldable entities or Media entities to achieve different use cases.
Take a look to the first 5 minutes of this video https://www.youtube.com/watch?v=vyav4VBuLng for more context.