I remember when Lawrence was using the hook grip in 2012. Knowing his coach and those that were with him in training that year, he started using it out in America as he was ruining his fingers with the tip grip. This was, I believe, purely down to the enormous amount of throwing he was doing in the build up to the season.
He switched to the hook grip so he could keep on throwing the amount he needed to since this grip took the stress off the tips of the fingers (which were the issue). He did lose a bit of distance immediately after switching to it, but he was able to continue throwing and continued it into the season with it as he had been training with it. I think his consistency of release actually improved as well.