#1 The A-Lister could win the match
Most of the WWE fans are assuming that Bray Wyatt will defeat The Miz at TLC because... well he's Bray Wyatt, who is probably the most over WWE Superstar at the moment. And this is why he isn't going to lose his championship for a long time. Vince McMahon seems so invested in Wyatt's character development that he isn't allowing wrestlers to beat him via pinfall.
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However, we have to admit that it's The Fiend (as a wrestler) who's over with the WWE Universe and not Bray Wyatt, except for his Firefly Fun House segments. Assuming that Daniel Bryan will face The Fiend at next year's Royal Rumble, we can say that he will be playing a role during The Miz vs Wyatt at TLC. What if Bryan comes to TLC and costs Wyatt the match, allowing The A-Lister to win clean? It isn't likely to happen but it's WWE, and they will want to make things rememberable for the fans.
How would this benefit the product? It'll strengthen Wyatt's feud with Bryan going forward and will make things more personal between him and The Fiend. Also, it'll provide a huge victory to The Miz. Since it's a non-title match, it wouldn't hurt anyone.