Day to day not so much unless you are in structured products/exotics as a structurer, at which point yeah its pretty important.
That said, already at masters level internships you could get asked much harder questions than what this article touches on. I got asked to prove the Cameron-Martin theorem once, I found that to be extremely difficult in a job interview setting.
In a linear rates shop (i.e. not trading options), almost all of the effort goes to tuning the deterministic bit of this equation. Thousands upon thousands of lines of code to do a problem that most books don't even mention behind giving the term a symbolic name!
And then if you do trade an option it's probably good enough to use an off the shelf model to work out your delta and so on.
If you're making markets or flogging exotics and structured products then you may indeed be wrangling this stuff all the time.
