You can mark them as shared if you want.  If they are shared though, then you will not be able to use the properties of the class withut declaring an instance of it within the method.

Shared is simular to having a global routine that runs stand-alone.  Memory doesn't really come into play just for making a shared method. 

You need to take special precautions when using shared methods in a multi-threaded situation so that they can be thread-safe.

Rule of thumb, don't mark it shared unless you really need to be able to run the code without having an instance of the class.

The UserController is done this way so that it can be used outside of the context of the running application.

The obsolete tag is so that you can see as a developer that you should be using a new method, but the old one is still there to keep from breaking legacy code.  Think of it as a waring that it is time to change your ways.