⇒ The responder is primarily looking for the Major fit. 
⇒ Without any Major, we want to play NT if we are (semi)balanced, but we want to play 3♣/♦ if we have a 6-card or 5♣5♦
⇒ With INV strength, we want to be precise and show a 6♣/♦ or a 4♥/♠. If we have neither, we can ask for the min/max with range ask.