I suppose that two might be better than one; however, when you go for the third perhaps it is best to stop.
Update: It does remind one of the limerick about Mr. Locke:
There was a young fellow named Locke
Who was blessed with a two-headed cock.
When he fondled the thing,
It would rise up and sing
An antiphonal chorus by Bach.
I guess the wife wasn’t into double penetration!