We love the kitchen for breakfasts, packing a quick lunch and occasionally having a smaller dinner in the room.
Our daughter is very young and any time we can avoid lines (food lines, ride lines, etc) the better.
By eating in the room for breakfast, our daughter can play with some toys, have her formula and then take a nap before we head out for the parks. Trying to do that while on a bus or waiting in line or in a cafeteria style restaurant for food, is very trying with a baby's patience.
Same holds in the parks for lunch. By packing a lunch, we can eat while walking her to sleep. We wouldn't attempt to make a baby, trying to sleep, wait in a food-stop for mom and dad to eat.
Lastly, we like to have a few small dinners to limit the gorging we do while on vacation. Eating out every night is just way too much food, even if you only get a main course.
Also the kitchens do save a ton of money. The last trip we just returned from was a 7 day stay at SSR. We only spent a total of $400 on food for 2 adults and the baby and that included about $100 for baby food. The food cost included eating dinner out 4 nights using DDE where we could and lunch at the castle with the princesses one day and one lunch at Le Cellie (sp?). While we don't go to WDW trying to save money, we were shocked at how inexpensive the food cost was while we were there.