Due to the defaults in `systemd.user.settings`, the default value when
there are no settings explicitly set is `{ Manager = { }; }`. This
means an empty file is created even when `systemd.user.settings` is
never used in home-manager configuration. Since user’s `user.conf` is
preferred to the global `/etc/systemd/user.conf`, this can cause any
values set in the latter to be discarded.
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