The idea of XMPP started long time ago around 2002 when there was an increasing number of instant messaging clients that couldn’t talk to eachother. You needed many many accounts and there was always functionallity differenses.
The same problem is now arising with the Internet of Things. There is so many different cloud systems talking care of things for you. XMPP-IoT provides means for all these systems and individual devices to collaborate just as you and I can be friends and start chatting.
The extensions created on top of the XMPP protocol all solves different usecases. Read, Write, consume