Hi Rama - you would typically usually use a continuous delivery when you are sending a delivery more than once per day. Recurring delivery is usually used for a delivery that is sent less than once per day. There are no hard and fast rules, but the continuous delivery is used to take some processing overhead off the system for preparing the delivery itself.
One other difference is the Recurring delivery is easier to quickly proof as there are no approvals tab in a Continuous delivery as it links directly to the delivery template, rather than creating a new delivery instance in the workflow. Continuous deliveries are also not linked with the parent campaign (operation) so you need to link these post-delivery if you require the Operation values in Adobe Analytics