Now, when we subtract 1, ask "are we in signed world or unsigned world"? If in signed world, we want the answer to be
0 ~= b0000000
-1. If in unsigned world we want the answer to be 255.
If we wanted to interpret the answer as signed , then we are free to do so. This automatically tell us that
0 - 1 = b0000000 - b00000001 = b11111111 =unsigned= 255
So, the advantage is that our operations don't care about whether the number is signed/unsigned.
0 - 1 =unsigned= b11111111 =signed= -1