Critical degrees are there because of 28 Lunar Mansions in your birth chart. When any planet is in the transition between Lunar Mansions (0, 13, 26 degrees of a cardinal sign, 8, 9, 21, 22 degrees of a fixed sign and 4, 17 degrees of a mutable sign), so it's stronger in your chart in a neutral way (neither positive nor negative), 0 degree Aries is purely Arian, 17 degrees Virgo is a Virgoan-Leonian degree, and 17 degrees Sagittarius is a Virgoan-Sagittarian degree, so if you have any planets in either 17 degrees Virgo or 17 degrees Sagittarius, these planets is in either Virgo or Sagittarius, but both have some Leonian characteristics