Here are some examples, for one, preorder on cdkeys and usually save at least 40% on the price. Pay for early headstart on an MMO and avoid the day one starter zone crashing and population overload
Conversely, you tell me, what do I gain by not preordering? Yes, if the entire planet didnt preorder then there might be an attitude shift in companies, but the rest of the world will continue preordering so thats a totally moot point. If I preorder and the game is rubbish, I refund. No harm done to me. If I buy at release and the game is rubbish, I refund, exactly the same, no harm done to me. So frankly, given the choice of preordering on cdkeys and getting a title on day one, 40+% (sometimes less than half price even), for a title I really want, I'll take the big discount.
Smart preordering is doing your research on a title, most of the people with bad preorder experiences are people who keep blindly preordering based on a promotional video. Like everything you buy in life, be smart about it. By the way, I've also just preordered my Christmas holiday this year