Comment by adamwathan

We use it in Tailwind CSS v4 for pill-shaped borders:

  .rounded-full {
    border-radius: calc(1px * infinity);
  }

...as opposed to what everyone has done historically, which is pick some arbitrary huge value like:

  .rounded-full {
    border-radius: 9999px;
  }

No real practical benefit, just satisfyingly more "correct".