1. The longer you wait, the more rational you'll be.
Contact someone - especially an ex - when you're hotly emotional leads to a lack of control over what you say. The more emotional you are, the harder it is to control what comes out of your mouth - and thus, the consequences.
When you have a period of 30 days where you instigate the no contact rule, you're generally in a safe spot to contact your ex. This is because 30 days is a reasonable time frame to allow yourself to re-establish your self-control after a break.
2. More time in "silence" means more curiosity from your ex.
People have a misconception that more time passing between when you break up and when you re-establish contact means your ex will stop caring about you.
This is FALSE.
The memories and experiences you have with your ex are PERMANENT. They are there to stay. It does not matter of 30, 60, 90 days, or even a year passes - those memories are forever emblazoned in his mind.
So are the feelings he associates with you. (Which is why you want those to be good feelings.)
In addition, time apart means curiosity building on his end. If you wait longer, he'll become increasingly curious as to what's going on in your life... and that will increase his chances of responding when you do break no contact.
3. The no contact rule allows you to break the pattern in your relationship.
People fall into patterns in relationships. If these patterns become negative, your relationship will turn negative. (I.e., you fight all the time.)
So when you go no contact, you have a chance to change the way you act towards your ex. You have a chance to see them in a new light.
And when you change YOUR behavior, he will also change his.
This is a natural human response. The stronger person establishes behavior in the relationship; the reactive person follows. You must be the LEADER in your relationship.
You must break the pattern by instigating the no contact rule. Then, when you've had time to change your way of thinking and behaving towards your ex, you'll be able to establish a healthy, harmonious relationship.
How long you go no contact really depends on your own personal preference, but 30 days is a general rule. It's a good place to start; from there, you can decide if you need more time.