That's great help, thanks for the explanation.
Reason I'm asking is I have a developer friend who is also very interested in Bitcoin, and would like to create a mobile app to deskill the use of Bitcoin, but at this stage it's just back of an envelope thing trying to grapple with the concept.
Thanks again.
One more thing, if you have any services which are sending you recurring payments, such as mining pools, then you must change your receiving addresses with those services.