I have always disliked this practice; in myself and others. Too often people think they're being more efficient, but in reality they're NOT working while eating, but using this time to do non-work that should be done elsewhere to begin with. (And I'm waiting for the downvotes by the same people who think, "Yeah, I know it says not everyone can multitask, but I'M not in that group...".)

Also, it smells. I know people don't think it does, or that it's not objectionable, but it's just another sensory input for everyone around them. People wouldn't give a second thought to asking me to turn my radio down; why should I not ask them to keep their smelly heated-over Lean Cuisine in the eating areas?