Why is this an issue?

A value that is incremented or decremented and then not stored is at best wasted code and at worst a bug.

Noncompliant code example

function pickNumber() {
  let i = 0;
  i = i++; // Noncompliant; i is still zero

  return i++; // Noncompliant; 0 returned
}

Compliant solution

function pickNumber() {
  let i = 0;
  i++;

  return ++i;
}