I have found deja vu to be useful in the present moment when my recollection sort of expands past the 5-10 second period. During the 5-10 second period everything lines up perfectly as recalled in the present, but say that my original "memory" happened during a dream. After the 5-10 second period in the dream my dream would continue with a possible outcome from my next course of action. I think I have to use an example, because I'm getting lost myself in the explanation.
I had deja vu a couple weeks ago. I remember that the original "memory" occurred during a dream. In the dream I said something where the person I was with reacted quite negatively and couldn't understand my point of view. So, in the present moment, I had 5-10 seconds of deja vu just before I said my poorly received comment. I recalled the outcome of my dream and chose not to say anything in the present moment. The rest of our carride together was harmonious and I still have the distinct feeling that it might not have been had I said what I said in the dream and still had the urge to say in the present moment.
Hope that makes sense!!