Tags are similar to what you do with multiple hardware but rather than selecting every device manually you can use a tag, to include all the devices with a specific tag. For example, you can use all server. With the field excluded hardware you can select devices, that you don't want to include, for example you want every desktop except one. You can also use tags when excluding certain devices. For example, if you have a tag "Do not reboot", one can select all devices to reboot, but exclude all devices with this tag to ensure that no reboot is performed there.
In the image below, all desktops are selected, excluding the ones on which Windows 10 is installed.
If you click on the tag or the eye icon, you can see to what devices the job is applied to. In this case, no devices are affected by the Tag.
If another Tag is chosen, it looks like this: