Here's a good overview:
http://blogs.msdn.com/dynamicscrmonline/archive/2008/05/23/microsoft-dynamics-crm-sales-process.aspx
From my experience, Stage workflows like sales processes can be useful; however, you need to carefully plan them out, otherwise, they can be counterproductive. For example, if you have 50 things happen upon a stage of an opportunity changing, you can create a lot of work that needs to be undone if you ever don't want these things to happen.
Don't over-orchestrate the process, keep it simple as possible.