If you have three price points, small, medium, large, where you move the middle will dictate how many of them you sell.
Even if you keep the small and the large at the same price.
For example, let's say that we've got $5 and $10 as these things. If I put the middle very, very close to the top, the top one will look like a steel compared to the middle cause it's only 10% more, and I might get a lot more stuff.
And so if I wanted to sell more larges, I would push the medium right next to it and make it seem like a no brain. Upsell psychologically. On the flip side, if I wanted to sell more of the middle one, I would expand the distance between the large and the middle, and so that this one would look like the more reasonable option compared to the premium price.
You should always have a very expensive thing to sell because you can drive more sales to the middle, while also allowing people who want to spend the money to go buy the super expensive.