If I would venture a guess, there have probably been more posts on the subject of back tension in The Shooters Forum than any other subject. Well, maybe allignment, and Terry's clock, but it would be close.
While I'm no expert in the subject, I think it's universally agreed, both here and other places I've read, that proper back tension is essential to accurate shooting, regardless of how long you hold at anchor.
My understanding is that proper back tension is achieved as a part of the draw, and not after reaching anchor. One of the problems that has been discussed here is how to keep from losing back tension when you hold at anthor, which would ruin your shot.