I always picture it as a degree that doctors get if they are going to run a hospital, a major community health center, government job, etc. It really depends on what your specific career goals are. If you are a doctor and want to work in public health you can certainly do so without an MPH. The reverse is also true, you can just get an MPH and work in public health, obviously. Although the first, I believe, opens more doors than the latter.
I have considered different combos of the above since it is an area that interests me and have come to the conclusion that an MD will suffice for my career intentions. Although, I am currently obtaining a BS in PH.