I'm a programmer by profession and game-maker by passion and Freespace modding taught me plenty of skills and knowledge I am now using for my other projects. I made some small games in Unreal Engine 4 and Unity and even developed Heroes III-like multiplayer game for Android (I didn't release it - it was my thesis project).
Generally if you Fred something more complex than defending an Orion from waves of Seraphims, something that involves use if scripts, variables, creation of various game mechanics, it gives you general understanding of how game engine works, how to handle different issues and what to do to make your missions/mods/games playable and enjoyable. When I first learnt Unreal and saw its blueprints, my first thought was - wow, it's almost like SEXPs in Fred, even better
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