I am studying crystals and I recently learned that there are 32 crystal classes. Most of them seem to be basic polyhedrons with prism/pyramidal/dipyramidal variants. I'm having some difficulty finding a clear-cut answer on what these classes mean. Certainly, they don't represent all crystal structures, but all crystals are supposed to belong to them. Since there isn't much information on the internet, I'm left wondering how these minerals are categorized into crystal classes, or how useful the classes themselves are.

So in short, what is the significance and extent of usefulness in having crystal classes?