InputAttribute is used by the state to gather input value that will be used in the state processing, or to be included with the external web service call.
The checkbox indicates whether the value entered in the "input field" should be treated as "<i>session variable name</i>" when checked, or "<i>static value</i>" when not checked. When checked, the session variable name will be used in retrieving the value from the session variable.
In either cases, the value will always be persisted for durability across session.
Also, see OutputAttribute.