When you open a fresh jar of peanut butter do you only work through one side until it is completely empty then start on the other side?
Or when you get those shallow tubs of hummus does it have to make it back home undisturbed? Then one of the baggers at the grocery store shoves it sideways into the bag completely ruining the symmetry.
Food should be finished at the same time. You work gradually around all of your sides and main dish so you have exactly one bite of each left, and then you finish your plate.
My SO drives me nuts because they can just eat the entirety of the main dish and then eat all of one side, and then all of another.