I cannot even conceive of a time when I would stay onsite. I cannot fathom paying the price they ask to put all 4 of us in 1 room, when I can pay 1/3-1/2of that price and have mimimum 2bdrm condo with full kitchen and washer/dryer through skyauction. If I want to pay roughly the same price as a room at the All Stars (or much less, depending on what "season" it is) I can book up to a year or more in advance and reserve a 2 or 3 bdrm condo, with free internet and long distance included, at many of the area resorts such as Windsor Hills, Emerald Isle, etc.
You have to understand that for me and my family, the magic is in space and amenities. Not only do we not mind renting a car and driving, we prefer it! The WDW busses, with no seatbelts for anyone (especially infants and young children) and some people with no seat at all, seem very dangerous to me, and I prefer to have my family seated and belted in. I am delighted that I don't have to join the thousands of people standing in line for busses when I exit the park at the end of the night. If we are hungry when we leave, we can stop and grab a snack, or go back to our full kitchen and make something to eat . Most importantly, I can relax leisurely in my pyjamas and have my coffee in the morning. I don't have to get showered and dressed, and stumble to a food court. I don't have to spend outrageous amounts of money to feed my family eating out for every meal.
Last time we went, I packed cereal, microwave popcorn, peanut butter, margarine, Pringles, etc in our bags. At the grocery store I spent $100 or so and got some fresh fruit, bread, bacon and eggs, etc. We didn't eat "big" meals, but we had all breakfasts, a lunch or two, and some snacks. What we save on not having to buy all our meals more than pays for the condo and parking! We save a ton of money on the meals we do pay for by eating some of them offsite. We absolutely LOVE Golden Corral, and always have at least two meals there during our 9 day stays. Love Cici's Pizza, too. It is not gourmet pizza by any stretch but we enjoy it, and feeding a family of 4 for under $20. is a definite bargain. It takes very little time as it is a buffet, so no waiting for your meal to be prepared, and everyone can have as much as they like.
Huge convenience having your own washer and dryer. Don't have to worry about bringing home dirty laundry and don't have to pack as much, either.
We also recognize that there is much more to Orlando than just the WDW parks, (as a matter of fact, we prefer US/IOA!). We spend more time at other parks than we do WDW and offsite is more convenient to US/IOA/SW so it just makes sense for us.
I have never stayed onsite so I can't give you a comparison, all I can tell you is why we enjoy offsite!