Do No Spend Days Work?

One of the little personal finance tips and tricks you see around the blogosphere is the concept of the No Spend Day. The idea is that you have at least one regular day (usually on a weekly basis) where you spend absolutely no money no matter what. 

My questions is, do these actually work? 

Say I need gas in my car, but it's a no spend day for me, I would not put gas in my car. I would make it stretch. Then tomorrow, I would still need gas. The fact that I had a no spend day doesn't help me out here because I have to spend the money at some point.

I can see how this would work from the perspective that some people do a fair bit of shopping or impulse buying, but I have a feeling that it would end up being situation specific. 

I'm going to undergo a little experiment and implement some no spend days for myself. We're going to start with next monday and go from there. 

What do you think? Have you tried a no spend day? Does it work for you? Is it pointless? Comments are always appreciated!