I have a bunch of these "_embedded.jpg" files alongside my other originals (RAW + JPEG). What are they and why were they created?
If you're using the "Camera" developer, Shotwell extracts the embedded JPEG from the RAW file and places it beside the file. This JPEG is then used to display the RAW photo.
There has been some traction on changing this behavior to display the embedded JPEG without extracting it. See this ticket for more info: Camera RAW developer wastes disk space by extracting embedded JPEGs
Edit: It appears this bug has been resolved; bugs related to shotwell are now here: https://launchpad.net/ubuntu/+source/shotwell/+bugs?field.searchtext=jpeg