It is an exclamation point! Its whole and total purpose is to end a sentence or phrase to express a powerful feeling. You only need one. Any more than that is redundant. Suppose you feel the sentence warrants more than one; you should use your words to convey the strength or importance. You may even want to use bold print or underlining.
Frankly, using more than one exclamation point can be mistaken for shouting, so why would you want anyone to think that you are angry with them when you are not!?
This brings me to the interabang. An interabang (or interrobang) is an exclamation point, and a question mark together. Some will argue that the exclamation point is fine on its own, even at the end of a question statement. However, having the question mark there clarifies that the sentence is indeed a question, and the exclamation point shows it is being asked with strong feelings. Even so, there need only one of each.
I know this post is very short this week, but I wanted to share Victor Borge's Phonetic Punctuation because many of you most likely have never seen it, and I find it quite funny. Please, enjoy! Love Lots; Smile Often MommaHattie