Can anyone list out exact differences between Interaction Q and workbin, When we place Interaction in Workbin, does it save the interaction in UCS or IXN DB?

Yes it will be in the interaction DB  until it is markdone/stopped and it will be stored permanantly in UCS DB with status updates.

Only difference is, workbin is where you will save all the email drafts for later processing. You have to pull out the draft manually inorder to complete it. Interaction Q is where all the incoming emails will be sent to and it will be routed to agents accordingly as per the strategy.