Standard question about lower GF-LOW settings: why would you want to on-gas more? The point is to get up shallower where you're not on-gassing.
Standard answer ;-) : You never want to on-gas more. You want to keep fast tissues from bubbling too much, in order to avoid an early in-water DCS hit. His specific problem is that due to high work load in a short bottom time, his medium-fast tissues may be more saturated than usual compared to a relaxed dive of the same depth and bottom time. Of course it's a trade-off with slow tissues on-gassing, and GFlow=50 is already a lot more conservative than standard Bühlmann "GF100".