I saw sa video ni Steve Gadd, In Session...he was doing a groove open-handed and it really looks natural for him(ofcourse, Steve Gadd eh). He was asked why/how he did it. Ndi ko lang matandaan sagot nya..anyways, i'll try to watch it again and share what he said. Perhaps someone could share what he said there, to those who's seen it, too.
Anyways...for me, playing open-handed is not necessary but it's important. If you're used to play the other way, there's no need to shift. As John Tempesta said during his clinic here, "Stick to your guns.". But ofcourse it's important for drummers to be ambidextrous, it helps you with your independence and other things. Plus it gives a different feel when you play open-handedly, parang yun yung sinabi ni Mr. Gadd, as i faintly remember.