Bidding Three No Trump in a cuebidding sequence shows that one has extra values and that one is serious about trying for slam. If one bypasses Three No Trump in a cuebidding sequence, one is not serious about slam and if partner continues cuebidding, he is serious.
When a partnership has a four-four or a five-four major fit or better, one never wants to play in Three No Trump. Therefore, Three No Trump is not to play and is available in this way.
A five-three fit is only better in Three No Trump if there is no dummy reversal, if the short trump hand cannot ruff and if all side suits are adequately stopped.
The word “never” in bridge always has at least one exception, and that is when there is a four-four fit, when neither hand has shortness (both four triple three) and when all suits are adequately stopped, then and only then, Three No Trump is the place to play.
However, this is often difficult to discover, and a four-four major fit is usually played in the major with the hope that partner’s hand may have shortness. In a five-three fit, short hand ruffs occur in the hand with three trump. In a four-four fit, either hand can be made the short-trump hand, and then the other hand is used to draw trump.
The bidding: A four-four major fit is always better than a five-three major fit because of the short-hand ruffing reason above and because the five-card major when it is a side-suit gives two discards. A four-four major fit will usually result in a trick better than a five-three major fit.
So when North opens One Heart, South knows they have a Golden Fit in Hearts, but he still responds One Spade. North now knows they have a Golden Fit in Spades and can re-evaluate his hand high enough to force game opposite a minimum hand from partner. Three Spades would be invitational so he manufactures a Three-Diamond bid.
South shows a preference to Hearts over Diamonds, and then North sets the trump suit as Spades. The bids that follow are a cuebidding sequence. I would not be surprised at all if either partner threw their hands in the air in confusion. However, North discovers that partner has first and second round Heart control and second round Club control so he can bid Six Spades. The partner who learns enough from the cuebidding sequence must take charge and place the contract appropriately.
The Lead: The Queen of Diamonds is a natural top-of-a-sequence lead.
The play: Declarer must play the trump suit carefully. He plays the Ten of Spades to the King and then a small Spade to the Nine. He loses one trump trick and claims.
Result: Six Spades making for +980.