Provide deeper reasoning for SubscribeOn/ObserverOn/Subscribe pattern guidance

[LeeCampbell]

There is a fair challenge of the guidance on stackoverflow. http://stackoverflow.com/questions/34675045/should-subscribeon-and-observeon-only-be-invoked-by-the-final-subscriber/34699242?noredirect=1#comment57305296_34699242

Perhaps showing the work executed on the threads as swimlanes or sequence diagrams might help explain the issue. It may also help illuminate when the guidance can be ignored.

Other resources - http://introtorx.com/Content/v1.0.10621.0/15_SchedulingAndThreading.html