I guess it depends on hos slow 'slow' is. I ususally try to keep a flow in my techniques, which means that I have to ajust my speed to my own and my uke's abilities. If I practice a technique that I'm not familiar with, or if I'm focusing on some specific detail of the technique, then I must lower the speed to a level where I can keep a god flow yet still manage to be 'ahead' of the technique in my mind. I seem to have a 'minimum speed requirement' in order to maintain the flow, but I suspect that as I get better I will be able to do the techniques even slower - and still maintaining the feeling of flow. (this demands an equally good uke though). At the same time, I will probably be able to do the techniques faster while not loosing control.
Very important: It should never be so slow that it is divided into 'sections' with a pause between each section. Then you become too focused on the nitty-gritty details, instead of actually 'feeling' the technique.
Just my thoughts on the matter.