Soft-release buttons serve a utilitarian purpose as well as making a visual statement. Many Canon/Nikon large SLR cameras as well as other modern cameras, have a rubber o-ring under the shutter that gives a softer feel and reduces pressure to make an exposure. The purpose is to provide a compression barrier between your finger and the firing mechanism. Adding a soft-release distributes pressure over a larger surface area allowing more control when you activate the shutter. Additionally, there is an added benefit of reducing shake blur because soft-releases allow you to build up tension in a more organic way instead of mashing your finger onto the button, like so many point and shoot cameras.

*Camera pictured not included.