In the Super User Tour it says
Accepting doesn't mean it's the best answer, it just means that it worked for the person who asked.
On the other hand, this help answer states that
You can also accept your own answer, but you must wait 48 hours to do so. After all, someone else may come along with an even better solution to your problem!
Isn't that contradictory? If accepting doesn't mean to mark the best answer, why do you need to wait until you accept your own answer because someone might come up with "an even better solution"?