Since there have been some good suggestions, I feel I'm not hijacking the thread by asking why segmented trays exist anyway?
I certainly remember TV dinners, I thought of them as cool and a treat. I also remember the larger version, plastic by the time I encountered them, in the Army. There it's easy to guess that they serve as a form of portion control, and to give the server, in my experience a minimally-skilled kp, a target to hit with his serving spoon. Were they ever used in commercial cafeterias?
The TV dinner tray usually had 3 or 4 compartments, with diagonal divides, like a very shallow vee centered on a long side of a rectangle. Aside from neatness, very appealing to a kid and perhaps a soldier struggling with an unfamiliar cuisine--who might try this so long as not contaminated by that--do they have other advantages I haven't mentioned?