It's often used to describe a person, event, or experience that is exceptionally entertaining or amusing.
For example:
* "That party was a hoot and a half! We laughed all night."
* "He's such a hoot and a half! I can't stop laughing around him."
* "That movie was a hoot and a half! I couldn't recommend it more."
The phrase emphasizes the intensity and high level of enjoyment associated with the subject.