In general, the Dining Plan is more about pre-payment, UNLESS you have Disney kids (under 10), proportional to the adults in your party, and you do character meals.
There is almost no realistic circumstance under which the Quick Service Dining Plan is "worth it," paid for.
The regular Dining Plan is $64 for an adult and $23 for a child. A few select meals, and you're ahead, due to the inflated pricing charged by Disney for those meals when paid for cash. The H&V Fantasmic package is a perfect example -- dinner for an adult on the package is $58.58, and the child is $36.21. So, for an adult-child combo, you're already "up" $8 on the day before you eat any QS or eat any snacks. While a somewhat extreme example, it's not the only character meal going where paying a day of
DDP for the child is cheaper than paying OOP for that character meal, and it's not hard to break even with the party's adults at the same meal. Tusker House breakfast is one of the least expensive character meals; it's $31.95 for an adult, and $19.17 for a child. The kid needs to come up with $4 in value for a QS meal and two snacks in the course of the day; the adult is more likely to break even. But, again, that adult-child combo comes out ahead.
At non-buffet, non-character meals, it really depends on if the Dining Plan meal composition fits how you would eat, and the specific eateries you choose. It's hard to make somewhere like Beaches & Cream "worth" the value of a Table Service credit under DDP.
It is very rare an all-adult party is doing more than pre-paying on the standard DDP. The specific combinations of meals/food required get pretty specific.