Believe it or not potato guns in one form or another actually have some useful purposes. Shortwave radio hobbyists use them to shoot antennae wire into the tops of trees to get better reception. Very large versions are used to launch explosives in mountain passes to trigger & control avalanches. There are combustion guns used my farmers & airports to for pest/bird control. Pneumatic spud guns be used to shoot T-Shirts & promotional items into football stands & bleachers. Pneumatic guns can also be used for confetti & stage effects indoors. There are even professionally manufactured pneumatic guns that are used in the motion picture industry to simulate bullet hits during 'shoot out' scenes. Low powered pneumatic cannons could be used in paintball tournaments. And then of course this doesn't even include the pure entertainment value that these hold for the owner, shooter, & viewer.