From what I know, the proponents of FS believe that one's belongings are tied to their owner by an invisible thread, and the more belongings a person has, the more complicated and stressful a person's life is (the threads are harder to keep track of, etc). Or something.
Now, I'm not one who'd agree with the mystical attributes of having running water (a fountain) in the Northwest corner of my living space, etc, but I'm definitely in real agreement with the belief that belongings tie a person down.
I'm a slowly recovering packrat, and with my GF's help, I'm freeing myself of alot of junk that I just don't need to have in my possession. I went thru an office box last night that was about 3/4 full and separated out a few pounds of paper (some of which I'd never looked at before), and hopefully by the time I'm done with the decluttering project I'll have eliminated another few office boxes worth of stuff.
It's truly freeing. And there's not likely to be another downward spiral into perpetual packratism, either, since it's going to be much simpler to choose which items to keep. Before, there was inertia to 'hold on to' things, because I hadn't looked through them and decided what was important. Now I'll know what is important, and there will actually be some pressure to get rid of stuff that I truly don't need.
It should be really nice. More on this as the project progresses.