A sale doesn't save you money if you weren't planning on buying it in the first place.
This is true, but since Amazon sells a larger variety of products than any retail store in the world, you can easily buy from them things you already would have. I have a free Amazon Prime account and regularly get Amazon gift cards from reward programs and other things, so buy everything I can at Amazon, from toilet paper to cereal to tools...
At this point, I'm wishing I could opt in my Kindle 3.