Infinitude of Primes

Is the concept of infinitude of Primes necessary? I don’t seem to get the purpose of including that information in the Quant Flashcards and Quant Mountains. Is that concept necessary for the test?

I think it’s just telling that primes are infinite and that the frequency of primes get smaller as the number increases, if I’m right. This is worth knowing, but shouldn’t be too hard to learn.