'mix run' and :build_embedded = true

Normally mix run recompiles the code if there is a need.
But when I set :build_embedded = true in mix.exs then suddenly this behavior changes and no attempt to recompile the code is made.
Why is that? How are these 2 things related?

It was because build_embedded copied all of your app contents, without symlinks, to _build. That operation could be expensive and therefore had to be opt-in.

However, copying was made fast enough so we don’t have to care. Therefore :build_embedded has no effect from v1.5, and you don’t need to worry about it anymore.