This sounds highly useful for changes you can do in a few hours. Or for toy projects where I can keep the whole application in my head. I have no idea how this

This sounds highly useful for changes you can do in a few hours. Or for toy projects where I can keep the whole application in my head. I have no idea how this should work on a big refactoring where you touch every single one of your.. say 200 files and add something to every single method. (Don't ask, assume a change that moves every single primary key to a composite key, so every getX(id) would become getX(id1, id2)). I mean, we were multiple people - we split out the work because a lot of it wasn't even very error prone, but this took days (ok, weeks). Are you supposed to just not commit or even show the stuff you did to the others? (Yes, there were many, many reviews and pair programming sessions in between). Of course this was on a feature branch. Yes, it lived too long, yes there were still bugs at the end when we fixed the tests. I don't think it would've gone better or quicker if we had meticulously broken down the exact same change (add an id to every getter and setter on controller and db-layer level). Actually we tried - and as expected it took deep dive through all layers.