I liken WDW to a cruise ship. (I have been on one cruise long ago with my parents when I was in highschool). My parents have been on a couple, and we discussed how much WDW services have in common with the cruiselines. That is, if you stay onsite, if you eat on site (especially the
DDP), if you take advantage of ME (Magical Express), and if you use Disney courtesy transportation, then you arrive into an all inclusive, aiming to make it as hassle free as possible vacation.
If you fly, then you will check your baggage at your departure airport, and the next time you see it, it will be in your room at your resort. If you fly, you can get off your plane, walk over to the shuttle buses, which are nice luxury travel coach style buses, equipped with bathrooms, a welcome movie to entertain the kiddos, and relax as you don't worry about how to get where you are going and are taken to where you should be. Upon check-in, you may be able to have your room right away (depending on arrival time), and if you aren't, bell services can store your carry on items until you can check in, and if you are willing to tip them, they will deliver them to your room for you. Meanwhile, you have been givin' your key to the world. If you opt for charging priveleges on your key and if you are on the DDP, you will literally not need to carry anything else with you anywhere. (Most will have their supplies, of course, but the point is...) Now you can go make use of the resort facilities or go to the theme park of your choice. Anywhere you go, you use your key, it is admission to the parks, it is a dining card, it is a credit card. If you make any purchases in WDW, these can be delivered to your resort gift shop, where you can conveniently pick them up the next day, so you don't have to carry them around the parks. Courtesy buses, boats, and monorails will take you whereever you want in WDW. You need never worry about how to get where you want to go, other than getting to the appropriate bus stop, launching pad, station. These services also provide the members of your party some independence from each other as well. If necessary, a part of the group could return to the resort, while the other pursued other plans, etc. As an onsite guest, you will also be able to attend Extra Magic Hours, thus increasing your options for touring the parks. Depending on your resort of choice, there are childcare options, which would even allow Mom and Dad a chance to have a break from the kids while breaking from everyday life, while the kids are thoroughly entertained Disney style. Additionally, there are other opportunities of outdoor recreation, should you so desire to have such a break, including boat rentals, bicycle rentals, mini golf, golf, etc. And again, these are all accessible using Disney transportation.
While many of these services are offered at offsite properties, it is the total package that really comes together to offer the partaker of such an offering a true get away from reality, a true break from the everyday routine (it's amazing how funny you feel when you actually drive a car again when you get home). When it is time to get home, if your airline is a participant in the baggage check program, you will be able to check your baggage in at your resort, and the next time you see it, you will be picking it up from baggage claim at your home airport. Your carryon items can again be stored with bell services. You will again be driven back to the airport on the lovely bus (which you may be a little sick of by now) and entertained again by an in-bus movie, which will have the departure theme to it. While certain vacation stresses can never be totally taken away, WDW has really attempted to alieviate them in most way thinkable to those that opt to stay onsite.
Additionally, WDW has gone to great lengths to continue the magic of the parks at the resorts, so that while your resort may not be "Disney" themed, it is still attempting to be a little larger than life, a magical break from reality, which really, is what we all are looking for during our vacations. It's the total package. I would highly recommend staying on property.