Well, recall that if we want to transform glucose into glucose one phosphate, we actually have to utilize and hydrolyze an ATP molecule. So normally if we want to transform glucose into glucose one phosphate, we have to use an ATP molecule. But let's see what happens in this particular reaction. In this reaction we do release a glucose molecule, we take off the terminal glucose. In the process, we add up a spoil group without actually hydrolyzing an ATP molecule and this creates an energetically favorable process. So we essentially bypass the process of using an ATP molecule by releasing the glucose in the glucose one phosphate form.