Is there a reason to not just cut chestnuts through before cooking them?
I've only ever roasted them, and there, you do want to score them at least enough to create a weak spot, since heat above boiling temperatures will come into play and they will burst. In roasting them, I think they'd be more prone to drying out if halved first.

A small serrated knife is a better choice than a big chef's knife for that task, in my experience. The score does not have to be all the way through, either.

I would think that halving them before boiling would tend to leach flavor (making "chestnut tea" from the boiling water) and that would reduce the flavor left in the nut. 

I'd also think that if boiling them, scoring beforehand might not be needed, as I can't imagine them managing to steam to the point of exploding in a boiling water bath. But I would probably try it with one nut, just in case I was wrong, before loading up a pot-full.

Mostly I'd be happier if the darn things were less prone to be moldy, which is really disappointing.