Hi Donna,
There are advantages to staying on and off property. Personally, I find that even spending a little extra to stay on property is worth it in my time. The property is huge and driving to and from a hotel off property can add to a long day.
When you stay at a Walt Disney World Resort, you have access to booking your FastPass+ 60 days prior instead of 30 days prior. This is a big difference especially during peak vacation times. You also have the ability to enter or exit the parks later than non-resort guests using
Extra Magic Hours. You also do not need to pay for parking at any of the parks.
If you are flying to Orlando,
Disney's Magic Express is include with your resort stay. This will take you to and from the Orlando International Airport. You will not need to rent a car during your stay.
Finally, on select days such as July 4th or Christmas, the parks can reach capacity and only guests staying on property are allowed to enter the parks for safety reasons. There is no exception to this even if you made Advance Dining Reservations or purchased a ticket.
Wishing you a magical vacation!
Beth