The main advantage is that the files will no longer show up in diffs and PRs. That means, for a PR, the number of files / lines changed will more clearly reflect the actual change.
https://bugs.python.org/issue45020
Frozen modules must be added to several files in order to work properly. Before this change this had to be done manually. Here we add a tool to generate the relevant lines in those files instead. This helps us avoid mistakes and omissions.
https://bugs.python.org/issue45019