Its both socializing, a display of authority, a portal for hub ideas, and a place for your questions to be answered! Not only that, questions you ask have your adsense code on them some of the time and you can profit off random viewers! *the last time I checked*
It originally started as a way for hubbers to create new hubs when they lacked ideas but has grown to be so much more then that. It is a very useful tool for many, and it can add a few cents to your wallet if done well!
Lastly, It does help your hubber score to create and to answer others questions, there are even accolades for questions asked, questions answered, and for author selected "best answers".
Hope that answers your question,