Vegetarian glucosamine is a good option for many people who are looking for joint health and prevention of joint and bone related illnesses. The issue with regular glucosamine is that unless the manufacturer guarantees that the glucosamine is made from shellfish, it is not suitable for those who don't eat seafood, meat or pork. For example, if the supplement is made from pig cartilage, Jews and Muslims cannot use it.
It can be difficult to know where the glucosamine is coming for sure if the manufacturer doesn't specify the source on the label. So vegetarian glucosamine is a better and safer option for people who want to make sure that they know where their supplement is coming from.