Hi Tommat,
I always thought it was not such a big thing myself, until I went to see Simon Phillips (from TOTO) and all of the sudden I understood what the advantage of open-handed playing was.
To move your right hand from the high hat (sitting to the left of you) to toms,cymbals, etc and the worst , to the China (to the right) becomes very,very hard to perform when the drumming has to be quick.
In other words open handed playing buys you more time!!!
Even when your drum kit (like mine) is not all that big (extended), the advantage is that you do not have to rush so soon "to get it all in", also it is slightly less tiring.
Unfortunately I have not (yet) reached the point of reaping the benefits and still have to stick(for live performances) to the old cross handed manner.
But one day...........
Cheers and happy drumming,
Harry