From Nothing But Shooters (NBS):
"If you tilt the Wii remote in the wrong direction, even in the slightest motion, you could be staring at the sky or ground while someone pumps you full of bullets. I tried using the Perfect Shot because I heard it was easier, but it's not. The main reason it's more difficult to use a gun accessory is because when you want to knife someone, you have to push the gun forward. Doing so may cause your aim to be off and make you miss your target."