One thing to also consider is how it affects flow from the outlets of filters at the top. I have two aquaclear filters on each of my tanks. With the water level down lower it directs flow down towards the bottom, and with it at the very top flow will instead flow around the top regions of the tank and not so much to the bottom of my tank (My main tank is 21" tall though i beleive). I use pool filter sand and find that it pushes it up into a big crater if the water level is too low, so i keep it above what will do that or place something there to break up the current. But basically if you find you dont get enough flow towards the bottom and want to try and minimize dead spots, dropping the water level seems to help that.
I try to keep mine as full as possible to keep as much water to dilute nitrate/etc levels, keep noise and evaporation down, and i also find with the water level below the rim my light shines excessively into your eyes as you look at the tank which is annoying lol I also resealed my 75 gallon with the intention of having it not leak unless water went right over the rim, where my 29 gallon will leak if the water level goes above the bottom of the trim on top. In the end, if it doesnt leak you cant really fill it too much. Just keep in mind that flow can be affected as well