Here's a very general way to think about this issue:
The more you tend to eat three meals a day on Disney property (hotels/parks), the more DDP may work for you. The more you tend to eat fewer than three meals a day, or have an inkling to eat some at a favorite off-site place (or even have something in-room), the more that pulls the equation back toward no plan (OOP).
As an example for my family, we're only planning to eat 3 full TS dinners on property, plus one CS lunch. Breakfast in room all but one or two days of a week's stay. Might visit a favorite pizza place outside WDW one evening. That tends to suggest OOP for us, and when I do the math, sure enough, OOP comes out (a lot) cheaper for us.
As someone else noted, DDP can work out to as much as ~$100/person per day, and in practical terms there's NO way we're dropping that kind of $ on meals alone.