A saw is a multi-purpose tool that is used to either process logs or to modify shotguns. Having a saw is a must if one is willing to create a complex base, as a saw can chop down trees, and if there are a lot of trees in your area, you can consider making complex bases because of your abundant wood supply. Of course, making a regular shotgun into a sawn-off shotgun is quite valuable, drastically improving the close combat capabilities.