Using pkgs.lib on the spine of module evaluation is problematic
because the pkgs argument depends on the result of module
evaluation. To prevent an infinite recursion, pkgs and some of the
modules are evaluated twice, which is inefficient. Using ‘with lib’
prevents this problem.
The difference between xsession and xprofile is that xsession is exec'd and xprofile is sourced.
So with xprofile all commands after sourcing will still be exectued. This allows for instance
autostarting of applications while configuring the start of a window manager via configuration.nix.
