As you well know, I went through graduate level math. Which is far more than most people will ever know, or have any desire to know. Most of it is spectacularly useless.
Yet in every single job that I've been in, I've had occasion to use advanced undergrad to graduate level math.
If you have the skill, you see how to apply it. If you don't, then you never realize that you had occasion to use it.
Cheers,
Ben