I'm assuming it would add loft compared to having a steel shaft in it. The graphite might add more forgiveness. Someone else could add to this, I'm actually interested in this for the 718 t-mb.

I'm assuming it would give it a higher ball flight and also be more forgiving. I'm actually curious to have others opinion on this debating one the 718 t-mb

Woah, depends on the shaft bud! There are shafts that'll raise your ball flight and a few that will lower it. I've never heard that putting a graphite shaft in it will make it more forgiving. Back a few years ago, it was the opposite where steel would be more consistent. With so many good graphite options though, you really have to experiment. I matched my T-MB 2 iron to my irons (C-Tapers) and I love the ball flight. Just talk to somebody in the know about your ball flight goals and what you're using your 3 iron for and go from there.