When we have finished decluttering at a clients home, I always get the same response: "I feel so much lighter now!" And it is true - decluttering your physical environment also declutters your thinking and emotions too. Here is a great article I found on Lifehacker.com that goes into this phenomenon in a bit more detail.
How clutter happens
You collect things for a number of reasons–maybe you think you’ll need to use it later, it has sentimental value, or you spent good money on it so you feel you need to keep the item, even if you haven’t touched or used it in weeks, months, or years.