The best explanation of the purpose of this class is that it solves Java Bug 6389107
There are many use cases where one wants to essentially have a Map<Class<?>, T> for some reason, but this causes all sorts of trouble since Class objects will then not be GC-able until the Map is. WeakHashMap<Class<?>, T> doesn’t solve the problem because very frequently, T references the class.
The bug above goes into a much more detailed explanation and contains example projects/code that face this problem.
ClassValue is the answer to this problem. A thread-safe, classloader loading/unloading safe way to associate data with a Class.