1. Best Buy has a rewards program when you preorder games, depending on how long youve been a member and how regular you buy from them.. you get a shit ton of cash back. Every 2-3 months I get about $180 back from Best Buy in reward zone. That I say is worth it.
2. Your supporting the developer by preordering their game, alot of the time they determine the success of sales based on preorder numbers. Also the earlier you buy the game, the more of the money is going directly to the developer. The longer you wait, the more money ends up just going to the location you buy it from (Best Buy, Amazon, Gamestop, Walmart)
3. You can play the game the same time as the initial rush (No risk of people spoiling it for you)
Those 3 points alone are enough to convince me to preorder/buy on day 1.