When you create an event and define it as "Treat it as Numeric" and then create a session attribute on this, it then treats the session attribute as a string. For example, if you create an event on basket value and then a session attribute on this, when you then sort sessions in a session list by basket value you will get - 10, 150, 20, 250, 90, etc. rather than 10, 20, 90, 150, 250. This makes it very difficult to find the highest basket values in your session list.