If you turn initial touch off you'll miss the expressiveness that many sounds can give. In my experience, even though organs didn't have touch response in the past, you can play them more creatively with a more tactile approach. The velocity settings (soft-med-hard etc) are a personal thing, and will vary with each player. Test each one out on your favorite sound. Play as softly as you can, then gradually try to increase the volume. See which setting gives you the more expressiveness.
In soft mode, very gentle touches will yield a louder sound, and sometimes a more brilliant tone, as the curve affects not only volume, but other elements of the sonic DNA. Loud settings require more force to get the maximum expression and volume for each sound.
There's no "right" setting - use the one that works best for you, but give it a try. It's built in to help get the most out of the sounds in your instrument.