I can't provide any negative experiences... how about some positive ones??
We placed our mobile order for lunch each morning while waiting at the bus stop or for the park to open. When our window came, I pressed the I'm Here, Prepare My Order” button about 15 minutes before arriving at the restaurant. Sometimes our order was ready before we even got to the restaurant, or if anything a short 5 minute wait. One time we had to sit for 15 minutes even after we got there (Cosmic Ray's) but we just grabbed a bench and enjoyed the sunshine.
We used this strategy at Tomorrowland Terrace, Pizzerizzo, Cosmic Ray's. and Satuli Canteen. We had table service meals for dinner each night so no experience using mobile order for dinner BUT I will say that the table service arrival procedure is also better because you can check-in before you get there and our table was always ready right as we arrived at the restaurant.