I finished weight painting but when I begin animating, I found out that some vertex group is missing a weight or some vertex group might be accidentally applying weight to other unintended area. How to find out the vertex group that might be using a particular vertex without clicking each one and look at the color?
See this answer. With the vertex weight panel, you can at least select several vertices and see, which bone is affecting them. Also, you can copy weight setting from the active vertex to all selected vertices. This is helpful e.g. for the head, where you like to make sure that only one bone alone is affecting it.