configured by <varname>Requires=</varname>, <varname>Wants=</varname>, <varname>Requisite=</varname>,
or <varname>BindsTo=</varname>. It is a common pattern to include a unit name in both the
<varname>After=</varname> and <varname>Wants=</varname> options, in which case the unit listed will
- be started before the unit that is configured with these options.</para></listitem>
+ be started before the unit that is configured with these options.</para>
+
+ <para>Note that <varname>Before=</varname> dependencies on device units have no effect and are not
+ supported. Devices generally become available as a result of an external hotplug event, and systemd
+ creates the corresponding device unit without delay.</para></listitem>
</varlistentry>
<varlistentry>