I have no idea if this is true because I haven't researched it, but my wife got it from her nutritionist.
She claimed that research has shown that those who eat one thing on the plate at a time (as opposed to bouncing around from one thing to another) tend to have fewer problems with their weight. I thought that was interesting because they were actually encouraging my wife to eat one thing at a time, and in a particular order as well. She asserted that if you eat all your vegetables FIRST, it has a tendency to process better in your system.
Again, I don't know how much truth there is to it, but I thought it was intriguing. I have always been fairly OCD about eating that way ever since I was a child, and I have never struggled with weight. I eat all my vegetables first before eating anything else because I hate them and I want to get them out of the way, then I move on to the good stuff.