If you attach your light to a Picatinny/NATO rail on the side, it will stick out quite a lot. A better position is 45° on the side because it fills the space on the rail better.
Why should you use this mount? I'm glad you asked. With this mount, the flashlight is positioned slightly higher than your barrel. If you rest the barrel on a barricade or any other object, the flashlight will not get obstructed, and you will still be able to blind the enemies with as much light as possible. If you go for the more traditional 3/9 O'clock position on the side, your flashlight can get blocked easily, and you will have to tilt the rifle to the side.