No where near the stability of a tripod. If you are shooting HDR or EnFuse multiple shots, you will still have to align them. It is definitely better than handheld, but at the cost of awkwardness. It can get in the way in crowds almost as much as a tripod. It can also trip you up if you are not careful. It adds weight. You can use it with a quick mount, but it can be a handful mounting and unmounting, which presents its own problems.
In a museum, or other venue, that doesn't allow tripods you will appreciate the added stability (especially if you can wedge it up against something stable). The answer is yes and no. It can be a help and a hindrance. I am at current experimenting with a small tripod for use as a chestpod instead of my monopod.