In some situations it is useful to know if a used classloader is still live/valid. Especially with dynamic class loaders it happens that a classloader gets invalidated but is still in use. In such cases the client of such a classloader should be able to detect this and reload classes.
One use case is scripting in Sling: we have the JCR based classloader and for example compiled scripts. A JCR classloader gets invalid as soon as something changes with the classes it has loaded in the repository. In this case the jsp script engine should reload the compiled classes