I'm sure the purpose of jamming the signal is more likely to do with ideas such as if some nasty person figured they could easily guide some nasty device with a slightly hacked GPS to cause mayhem then it might be a good idea to be able to jam the signal to prevent it, no?
Even some of us who work on interesting hacks to publicly available electronic systems for security purposes are unlikely to know to what use our work is ultimately going to be put - the programmers get asked "please can you make it do x" and generally feel disinclined to ask "why?", a more appropriate response being "sure, when would you like it?". Personally I don't even think about it, I just do what I'm asked.