When your toilet tank fills, so does the bowl. The bowl however fills faster than the tank, and gets full first. So until the tank gets full, the water sent to the toilet bowl goes down the drain. So, consider getting a fill cycle diverter. It will reduce the amount of water sent to the bowl, and thus the wasted water. Also, because you reduced the tank's volume, you reduced the amount of time the tank takes to fill, which also in turn leads to less water wasted.