By the use of this phrase to open or close a statement, the user acquires or asserts a pleasant, folksy authority. Sometimes paired with "boy" for added authority and folksiness (see example).
Frequent famous users include Cris Collinsworth and Hank Hill.
"Boy, that was a heck of a down field block by Michael Vick, I tell you what."
"I tell you what, the Seattle Seahawks came here to play tonight."