Can someone explain please the point of embedding bin data into a binary, vs just bundling those assets and opening as a file at runtime?

Convenience. It's easier and more foolproof to give someone one file than it is to give them a directory.

The landscape of tools supposed to solve that problem isn't great. Things are changing way too fast with projects being archived or deprecated with mention to migrate to another solution which after another year is deprecated again. Because of those issue, I've went with go generate which isn't ideal but is at least stable. That proposal would be a game changer and hopefully it will become a reality as Brad is quite a prominent figure in the Golang world.