What are the pros and cons of teaching multiple sessions of the same course?
I've done this.  The big con is it can be incredibly boring, but maybe that's just me.  And agreed, what did I say to the one class and not the other?!  The big pro is it can help you refine your materials and teaching methods.  I've had two of the exact same classes taught in the exact same way produce very different results.  

Write some things down before you start.  If nothing else this becomes a checklist to get you through the semester.  Goes a long way to keep from getting confused about what you did or didn't cover.