It would be mostly useful if we want to avoid situations with having 2kkk + gold on your account however, it would be also useful to let us see estimated gold we're supposed to earn if we sell everything from our shop. It would be also beneficial because more often than not I double check all prices on items in case I put something with an incorrect price. Why waste that time if I could see the amount of gold I'm supposed to earn let's say on the bottom of shop window before I open my shop. It would be a cool little thing to have, that would give players a clear user interface.
My raid design: THE NEXUS