I hear that question frequently in math. It grows old. Do they ask the same question in English class when studying the poetry of Emily Dickenson? (Related post here)
Anyway, I wrote previously about finding the WWII pictures of my grandmother in uniform. I've been doing some non-scholarly research about the work she did in the British Army and came across a site dedicated to the women of the Auxiliary Territorial Service, to which nana belonged. And what do I find there? This tidbit of information about women in anti-aircraft artillery units, of which nana was a member:
Another instrument that was used by A.T.S was the kinetheodolite. This was only used at practice camps but this was based on the theories of cinema and theodolites combined. The operators would film mixed battery detachments firing at drones on the practice camps. The films were taken back in the evening to the camp headquarters and the operators would use the measurements taken, together with the film to work out how close to target each team was firing. This enabled teams to adjust their procedures in order to become more accurate. The work of the kinetheodolite operators was very mathematical and only those who were very good in this subject were able to cope with the calculations that had to be made each day. (emphasis mine--Darren)
So when are you ever gonna have to use this? Maybe when you're trying to defend your country from attack by a ruthless enemy!
Bottom line is, I don't know when you're "ever gonna have to use this stuff". But isn't it good knowledge to have, just in case? And why cut yourself off from fields you don't even know about yet? I'll bet the women in school in 1930s Britain never thought they'd be using math to help shoot down Nazi aircraft.