A “soft shutter release” usually isn’t soft because of the material. Many are made of metal or other rigid materials. The term generally refers to the shooting feel: these buttons are larger and sit higher than the camera’s standard shutter button, so some photographers find they can press the shutter more gently and with less disturbance to the camera.

The claimed advantage is a smoother, lighter-feeling press that may help reduce camera movement at the moment of exposure, especially on cameras with small shutter buttons. Whether this helps in practice varies by user and camera design.

As for half-press operation, the button doesn’t change the camera’s shutter mechanism itself. It mainly changes the surface you press. Some people may find the raised button improves feel, while others may feel it makes the half-press less distinct. It’s largely a preference and ergonomics accessory rather than a universally necessary upgrade.