How come in anime they always scream out the name of the attack they're using

One time I asked a guy at EB Games this because he was playing with his friend in the store and they were yelling out attack names. He powered down his Kamehameha and looked at me and then explained, "The reason people shout when they attack is because it allows them to further their power. Have you ever punched anything? You involuntarily go MMMPH. It's like that, but voluntarily. The force you deliver is doubled through this simple action."

Quote is probably a little off, it was like 9 years ago, but that's the gist of what he told me.