Adding gauge wheels to the back of a box blade accomplishes a couple things: First, it controls cutting depth very well and does an excellent job of leveling and, secondly, it puts weight back where it does the most good.
I was obsessed at one point, with adding weight to my 7' 600lb box blade, from reading here on this forum. It would come in handy for bb operation occasionally, but I'd rather have it for the counterweight function. I rarely ever need more weight for bb function.