This is a very important question to ask when organizing your spaces. It is hard to know where to put something if you don't know why you have it, or how you use it. When you begin to remove excess stuff and organize, make sure to find the function of each item before keeping it. Here are a few questions to ask when trying to determine if you truly need the item.
-Have I ever used this?
-When was the last time I used this?
-What is this item's purpose?
-Will I miss it if it is no longer here?
-Is there a different purpose for which I can use this?
-If I decide I need it in the future, can I replace it easily?
Finding the answers to these questions will make it simple to let things go, or to find the proper place for them if you have decided they have value in your life.
P.S. Anyone else think of Schoolhouse Rock when they read that first question?