On the disneyworld premier pass page it says you get 20% dining discount. It doesn't list any of the restaurants so I'm not sure which restaurants are included. When you look at the Annual pass benefit guide for 2016 it says you get 10% dining discount and lists a handful of restaurants. The guide doesnt list any of the Premier pass benefits or locations. Since it is the premier pass...and it says 20% discount...are ALL restaurants available for a discount? Can you use the discount on snack carts/locations? This leads me to my next question. Tables in Wonderland offers a 20% discount, including alcohol, with a handful of restaurants listed and has a couple of blackout dates that fall into my trip dates. Does the Premier pass also apply blackout dates for discounts? Do I even need to purchase tables in wonderland if I get the premier pass?
The Premier pass page says "up to" 20%, not a universal 20% discount. Premier gives you access to Platinum-level AP discounts, which vary by level of discount and in Epcot, by meal and day of the week. The WDW AP dining discount is far more limited than what you have access to at DLR with an AP, particularly that there are no counter service AP dining discounts at Disney World, and no AP dining discounts in Magic Kingdom at all.
That's why many people purchase the separate Tables in Wonderland card (an additional $150 for APs.) It in general offers a blanket 20% discount at most table service restaurants (far more than the AP dining discount offers), including alcohol.
If you are doing a short trip, are not going to eat at many table service restaurants, are not going to eat at signature table service restaurants that are especially costly, or a combination of the three, you probably don't need the added cost of a Tables in Wonderland card. If you're going to have one or more ADRs every day, if you're visiting for a week or longer, and especially if you expect multiple trips within the next year, then Tables in Wonderland makes more sense. But it really depends on the restaurants that you and your family want to visit.
My partner and I are platinum APs and we are going through this whole decisional struggle now, considering whether we want TiW too. There isn't a one-size-fits-all answer, unfortunately.