Can someone explain use of these monitors?

could be used to places where projector is unavailable and device monitor monitor is too small. So might be used in meetings to output visual from small tablet or note pc. But yeah... would it be worse carrying it around? no. Might be useful to have in conference room... but projector would do better job.

Can someone explain use of these monitors?

Only after using a multi monitor setup you can really understand, this monitor is clearly to carry around with a laptop.