Describe some of the differences between using an Agile process and using a  Plan and Document (or Waterfall) process. 

The main difference (to me) is the planning phases are completely different between the two processes. Waterfall attempts to plan everything in advance while agile usually plans one sprint at a time. This includes; defining requirements, documentation, sometimes tests.

From my limited experience, projects that begin as a waterfall project end up having an agile style process anyways. It is rare for a project to proceed exactly as expected and managers are forced to improv to maintain deadlines and expectations.

In my opinion, a mix of the two processes is best. I think agile process falls short when a project does not have a clearly defined goal or roadmap while waterfall struggles to accommodate feedback or any sort of changes