I think clutter can be part of a poverty mindset - it can also be used to take you out of the "now" and being fully present. Even if someone doesn't consciously feel stressed around clutter, I believe at an energetic level, that stress is present.
I used to keep absolutely every book I owned, I had shelf after shelf of books, books, books, and I would panic when I thought about getting rid of them! Something shifted though, and a few years ago, I went through all of them and asked if I LOVED that book, and if I didn't - out it went! My son's preschool got them all, and made money with them at their yard sale. In the years since, I periodically weed through my books, and now, even if I LOVE a book, if I haven't read it in a while, and don't think I'll read it again - out it goes!
Clear Your Clutter with Feng Shui is one of the BEST books I have read about clutter, and reasons we have it, and how to clear it! It also introduces some feng shui principles.
My home used to be very, very messy all the time - really dirty. Since moving last year, I have kept my new place cleared - it makes SUCH a huge difference in how I feel. I no longer have my clutter to hide behind! There were so many reasons I kept a messy house, I have tons of stories, but will stop here. Clean and clear is SO much better for me.