Decluttering is a form of therapy. It's freeing to tackle boxes of junk you haven't bothered to unbox in years, go through it all, keep 5 percent of it and get rid of all the rest. It's as though you are not only purging physical objects from your possession, but purging needless clutter from your mind as well.
The same goes for organizing the stuff you do keep. As you set your stuff in order, you do the same for your thoughts.