In the game of Spades, sometimes I see a strong player bid such that the sum of bids is 14. This means that one of the contracts will be set.
In what conditions this "complete-to-14" bid is a strong play?
There are no hard and fast rules or heuristics for such a decision, but the following indicators will tend to be positive in such a circumstance:
When one is clearly the strongest player in the game.
Strong players play well and weak players play poorly, of course; but under stress of an overbid deal weak players can be expected, typically, to exaggerate their own worst tendencies: this is part and parcel of being a weak player.
In an underbid hand there are potentially 130 points available to be earned. in an overbid hand there will never be more than 120, likely less, points available. Anyone making their contract is thus automatically gaining on the field in an overbid deal.
In the most extreme case, where the opponents win the game if they make their bid and it is thus essential to set them, one might as well bid for the set and overbid the hand to 14.
When the hand demands it
If one's hand clearly is strong enough for a 3 bid with a chance at 4 tricks, but as dealer the hand is already bid to 11, a bid of 3 to overbid the deal at 14 seems in order. Someone is in for a nasty surprise and it doesn't look to be you.
When long in Spades
Holding five or more Spades in your hand, on an overbid deal, will definitely surprise someone expecting length tricks in Spades that are now vulnerable to your holding.
In addition to Forget I was ever here's answer, it's appropriate to bid to 14+ tricks where your hand is disproportionately strong by itself (like comfortably bid 7 or more) and no one bids nil. This doesn't happen too often, since monster hands for one player usually mean that someone else is bidding nil which can change bidding and play patterns.
Very strong hands often make your partner's hand much better. The fact that your hand has a lot of high cards and spades simultaneously protects your partners winners while promoting half-tricks into full tricks.
Imagine you have a monster hand like ♠AKQ7432 ♥KT3 ♣KQ ♦A which is worth easily 7 tricks (4.5-5 in raw spade power + 2.5 in side suits). This hand makes your partners lower honors relevant, so you can consider aggressively bidding to 8 if your partner bid 2 or more. Let's say your partner has bid 2. Your partner could have a hand bid conservatively with a hand full of maybes like ♠JT6 ♥AQ3 ♣73 ♦KQ432. Or maybe they have unfavorable suit distribution like ♠6 ♥AQJT42 ♣T73 ♦Q63. These are hands that can get anywhere from 1 to 3 tricks depending on how the cards fall, so they bid 2. Your very good hand maximizes these marginal ones, so you can consider bidding higher, even if it brings the total bid of the table over 13.
I'd also consider the aggressive bid to a sum of 14+ tricks if the extra trick would put my team over the winning scoring threshold. It is risky, so you probably wouldn't want to do this if you have a huge lead. But sometimes is right to go for the win now to deny your opponents any chance of a comeback.