Hi Usman,
In many cases, people do not open tasks directly against a monitor, so the default configuration is to not have an associated CI Class. They are often just tracked as Assets. An incident would then be opened against the computer (if anything) and the monitor would be described as the issue in the incident.
In the demo data, there are three monitors. One Model is set to behave as a consumable. The reason for doing this would be based your needs for managing Monitors. You might want to track specific monitors, which is how the higher end Monitors in the demo data behave. You might not track lower end models individually. You might instead work with them as consumables if they are not worth the effort to track individually.
