Whenever you find yourself at a lower level in any bracket, X amount of item levels is added to your items, making them more powerful and bringing them in line with the items available at max level. In the case of the 20-24 bracket, 1 item level is added to all items per level you are below 24. This means that if you are level 20, all your items gain an additional 4 item levels. At 22, you would get 2 item levels, probably making a lot of your gear superior. How the difference affects items is hard for me to say, as I haven't done extensive testing on it. All items react different to the increased item level, but to say there is no difference would definitely be wrong.