A monopod will generally buy you about 1-3 stops, depending on your skill. With VR, you can get another couple of stops, so the combination can be very effective. And all VR can be used on a monopod, where only the very expensive exotic telephotos support tripod enabled VR.
Ditto all the other reasons mentioned here. Even in situations where monopods are "legal" or "allowed" I personally do not like to use tripods in busy public places. And in other situations I want to be more mobile than I am with a tripod.
Plus, it is just easier and less tiring in the case where I need to watch a scene or support a heavier lens and body combination. Also easier to do smooth pans and maintain a precise focus point while following a predictably moving subject.
Monopods are cheap so it is well worth the investment to try it yourself. But give it some time to develop the technique. You may find this article very helpful.