network-services.conf currently says "start on started boot-services". This triggers a few jobs to run early during boot, in particular before the UI is up. The general rule is that we shouldn't be doing any work that isn't necessary to get to the login screen.

I'm not sure whether there's a legit reason to start networking stuff early. If there is, then we should document this in a comment in network-services.conf and justify potential impact on boot performance.