Pros:
You know earlier whether or not you’re going to the school so you can plan for this.
Your chances of admission are slightly higher – schools know that they are your top choice and that you will definitely go there. Later on, they risk you picking another school. If it’s kind of a stretch to get in, ED will definitely increase your chances.
Cons:
If you change your mind, it’s a contract so it’s hard to get out of it and go to a different school. If you’re not 100% sure that you want to go there, don’t apply ED.
THey make a decision based on your grades/scores through junior year for the most part. If you’re rocking it out your senior year and really increasing your GPA, or can go better on the SATs, then you might want to hold out for later and use your updated scores. Of course, when you apply ED, they may choose to roll you over into the regular deadline anyway and you can add this info at that time.