Quick question: Should we be replacing :biff.tasks/tailwind-build nil in our config.edn with :biff.tasks/tailwind-file nil or that something only new projects need to concern themselves with? I'm guessing that it doesn't really matter if I'm already getting by with nil, but just in case, I thought I'd ask.

You can ignore it. That option's only used if biff has trouble figuring out which tailwind binary to download.

Roger that!