VC, IS, OIS, whatever your particular camera or lens company calls it call it...does it help?
We know it helps, but by how much? Here is an image that I shot with the new Tamron SP 150-600mm F/5-6.3 Di VC USD Lens.
A rule someone made a long time ago was basically if you try to handhold, your shutter speed should be 1/your focal length as a minimum. So, if you are shooting at 600mm, your shutter speed should be 1/600th of a second as a minimum.
VC allows you to handhold at much slower speeds than this old rule states. Here is an image below that shows you how much VC helped me out in my situation.
This image was shot at 552mm and handheld (which I don't really recommend), but instead of shooting it at 1/600th of a second, it was shot at 1/30th of a second. Yes, 1/30th. I was only able to remotely pull this off by standing very still, bracing against a tree and using my lens' VC.
The other settings were ISO 100 and F/6.3. This was shot in Aperture Priority. In theory, I should've bumped my ISO up to give me a faster shutter speed, but VC saved me here.