There's even an article I read about this the other week, but I can't seem to find it ATM.
The challenge is that you have to be working on multiple work streams at once because so far Codex isn't great at not doing work you are doing in another task even if you tell it something like "class X will have a function that returns y"...it will go write that function most times.
I've found it really good for integration work between frontend and backend features where you can iterate on both simultaneously if the code isn't in the same codebase.
Also, for Codex this works best in the web ui because it actually uses branches, opens prs, etc. I think (though could be wrong) that locally with the CLI or IDE extension you might have to manually great git worktrees, etc.
If I ever find my self just waiting, then it always gives me an opportunity to respond to messages, emails, or update tickets. Won't be long now until the agents are doing that as well...
When i use that approach I end up merging one PR, then have to prod the others to fix themselves - resolving conflicts, removing duplicate code, etc - so it ends up slower than just running one agent at a time.
Like i said - maybe this is a problem on a bare repo? But if so, how are people vibe coding from scratch and calling themselves productive? I just don't get it.