Usually I neck carry if I do not have the option for a belt.
For instance, Nikki and I often wear sweatsuits or fleece wear if lounging about our cabin in the winter. No pockets, and a folder clipped to the inside of the fleece gets annoying. So, in that situation, I'd neck carry something.
Or, here at home, in the summer if wearing shorts and a t-shirt around the house, I may also neck carry a little blade.