[Sirtel]

Editing the file saves the changes you made in the file. Editing the metadata saves the changes to the Calibre database. For saving the metadata in the file itself you need to export or use the tools mentioned above.

In short there's a difference in saving the changes in metadata and the changes in the file itself. The editor (Edit book) changes the file, so no need to export or embed afterwards. "Edit metadata" changes the database, not the file, hence the need to export or embed.