This is precisely the kind of attitude that makes it so difficult for teachers who are teaching certain courses. I don't know how many times I had a student tell me he or she was never going to need the material I was teaching. In most cases it was an excuse for them to not have to learn, but that kind of thinking is pervasive. Even the parents, and unfortunately some of the teachers, will buy into it.
The simple fact of the matter is that all knowledge is valuable. And most students don't even know what they want to be when they grow up, so how do they know if the courses they're taking will be important to them?
Do welders need to take speech? They do if they ever have to teach a fellow welder a certain technique or skill. Speech helps everyone communicate better.
Do lawyers need to take biology? They do if they ever expect to properly prosecute or defend a person accused of a crime based on DNA evidence.
Do math teachers need to take a foreign language? They do if there's a chance they might have students in their classes who speak a foreign language?
I even had a student in PreCalculus refuse to sign up for Calculus during her senior year. She wanted to be an architect, but had been advised by an Industrial Arts teacher that she would never need Calculus. While it may be true that most of the heavy-duty math would be done by a team of engineers and most of her design work would be done on a computer, how could a course in Calculus hurt? She was extremely bright and had room in her schedule, but opted out. It's my personal opinion that every student should take the toughest courses they possibly can in high school. They are so much better prepared for anything that lies ahead.
Sure, there were courses I took that seemed irrelevant at the time, but it's amazing how much of that information I discovered I needed at a later date.
And unless you take a wide variety of challenging courses, you never see the interconnectedness of everything. I discovered this when I took a course called "The Brain." I needed all the biology I had learned because the brain controls every function in the human body. I needed all the chemistry I had learned because every process in the brain is chemically driven. I needed all the physics I had learned because the brain uses electrical impulses to work. Of course, I needed mathematics to do the science. But I also needed the social sciences such as psychology and sociology to further understand the workings of the brain. Environmental studies were also important because of the effects of that environment on the chemistry, biology, physics, and psychology of the brain.
Everything is connected. Every subject is important. Knowledge is never wasted. Learn all that you can because you never know what the future holds for you. And never tell anyone that something they've learned is irrelevant or that they will never use it. You really just never know.