For me, there are two times I use Dom space.

One is when I have a regular sub and am punishing her. I realize this is necessary for a number of reasons, but I truly despise having to do it, and thus Dom space. I find that I click better with my sub if I can just be me and not add a layer of play between myself and my sub.

The other time is when I am doing a scene with a sub that I have not bonded with. I guess this keeps me focused on the limits and the other pre-arranged things that I need to track. This allows me to step outside myself and keep an eye on both her and myself.