When we talk about reducing unnecessary spending, most often we think about money, but there are also other reasons to avoid buying things you don't need - even if you can get them really, really, really cheap.
By purchasing items I don't really need, especially cheap, low quality, mass-production ones, I'm encouraging a further overflow of this product into the market. I'm giving a hand to environmental strain and under-paid labor in countries like China.
When I buy things I don't need, I'm wasting valuable storage space, which is a scarce resource in a small house like ours. I don't want to end up re-arranging our furniture or adding extra shelves for the purpose of storing items I never use. We do have an outdoors storage shed, but it's meant to be a place for seasonal items and a stock for non-perishables like toilet paper, not a dump for things we mindlessly bought and never used.
I've also found that an excess of possessions has an effect of cluttering my mind. When I have too many items in my closets and drawers, I'm unorganized. If I have too many clothes, I'll put part of them away and only use a few items I love. I like to use one brand of shampoo, perfume, or body lotion at a time, and nothing grates on my nerves like a cluttered bathroom cabinet. I don't want to have trouble remembering which things I already have!
That's why I'm also careful about acquiring freebies or things people are giving away. For example, in a discussion of one of the posts here, I mentioned that we don't have a changing table, even though we could get one second-hand for free. However, we had to consider the fact that the baby's tiny room must already hold a closet, a cupboard, a guest bed, a drawer chest, and a crib. Putting a changing table in there would mean blocking the only bit of free space left.
Here's a useful article on the benefits of being more organized (hat-tip to LAF):
"How big is your wardrobe? Do you or your children own 30 pairs of jeans at $60 a pop because you don't keep up with the laundry or because your closet is so stuffed you can't find anything? That adds up to $1,800 worth of jeans. If you cut it down to even 10 pairs you would save $1,200. How many tops do you own? How about those shoes? Before you say, "There is no way I have that many jeans, shoes, or tops!" go count you clothes. You may be surprised..."
"Do you buy new items because you can't find something? The cost of things like tools, glue, tape, ropes, garden tools, kitchen items, light bulbs, batteries, office supplies and other things really adds up."
Keeping clutter under control by not buying items you don't need certainly helps you save money, but even more importantly, it preserves your sanity, your efficiency, and helps your run your home more smoothly. If you already have a lot of clutter, getting rid of it might involve a lot of work. Therefore, my solution is: don't let unnecessary items in your home in the first place - it will save you a lot of headache, time and money later on.