It alters the leverage ratio on the rear shock, so you might need to change the spring and damping rates.
Unless you drop the front yolks down the forks you alter the head angle, which makes the steering slower. If you do, you reduce the ground clearance by enough to take the fun out of hard cornering. You might also need to shorten the side stand.
Generally, unless you're shorter than about 5'0" you're better concentrating on your slow riding skills so that you don't need to lower the bike.