I just started out honing this week, so this will be a beginners point of view here.

I find using two hands easier for me because it allows me to balance the razor on the stone better. If I use only one hand, its only a matter of time before I tilt the razor and the heel is just riding the lip of the hone. I just put one to two fingers gently on the tip and this stops me from lifting up the tip and having the handle hit the table. For me its easier to use less and less pressure with two hands because it gives me more control and I won't end up see-sawing the razor on the edge of the stone.