What does documentation.nixos.includeAllModules actually do?

After setting this option (recommended elsewhere) my build starts failing with

function ‘anonymous lambda’ called with unexpected argument ‘utils’

in any one of several files included in my configuration. Before figuring out whether this is worth fixing, I tried looking at its description, but that’s not very helpful. What does it actually do? And what is baseModules?

I’ve looked for all the relevant keywords (“utils”, “baseModules”, “base modules”) in The NixOS manual and the NixOS modules wiki page, without finding anything.