This is only good advice in cube play, you will note modern decks do not take this advice and this is because in cube you very rarely face mirrors due to the card pool being what it is
It is a lot of utility and a lot of value
Deck weight is a major factor in determining what kind of opponents and decks you are matched against in the game, and this discovery has captured the community's interest
For example, blue provides card draw with cards like Consecrated Sphinx and blue countermagic like Mana Drain or Counterspell, black offers powerful spot removal like Fatal Push and has access to the best tutors in the game in the form of Demonic Tutor or Vampiric Tutor, and white adds board wipes (Wrath of God/Day of Judgment) and recursion in cards like Second Sunrise or Faith's Reward
This should mean big gains for key Modern cards that arent in Ultimate Masters , like Scalding Tarn, Leyline of the Void, and Surgical Extraction