If you invite me to a potluck style dinner and ask for something specific, I'll deliver. If you know what you want, it's yours. (You'll have your mac and cheese for Thanksgiving, Dad!) If you ask me to bring my favorite dish, I will disobey, because the veggie tray always gets eaten.
Years ago, after I had some baby or another, my mother asked me to bring an appetizer for Thanksgiving. She didn't care what it was. She didn't even mind if I bought it instead of making it myself. (She, too, had been the parent of young children and knew better than to expect anything elaborate.)
I was probably still trying to take off baby weight and thought it would be a great idea to stuff my face with raw veggies before the main event. Though "tray of raw veggies" isn't usually associated with a decadent meal, people loved it. The plate was empty and I was asked to bring it again the next year.
Potlucks without specific assignments tend to be full of decadent food, often loaded with cheese. A veggie tray is the perfect antidote. I also like knowing that I'm providing something for the quiet vegetarian who might not find many things on the table to eat otherwise. And I like to get a few servings of something healthy into my kids during a season of sweets and heavier food.
Veggie tray isn't exciting. No one leaves a potluck talking about "that spectacular plate of crudité," but it always gets eaten, so if you don't tell me what to bring, that's what you're getting.
What are you bringing to Thanksgiving dinner?