We had concluded last week, that when suits start breaking evenly go for the even break. Therefore, our sub-role of vacant places states that: Length attracts shortage and shortage attracts length - equi partition attracts equi partition.
Suppose in 6D contract if holding
West leads a trump, east follows 9D. Winning, when you lead singleton spade 6 to KS, east wins AS and plays second trump. Trumps break 2-2. So if clubs are breaking 3-3, you have your 12 tricks. When you cash QS for a heart discard, ruff a spade, return with KC, ruff 4th spade both defenders following. On AC both follow and on JC, east produces a low club, what are the odds?
West has produced 4 spades, 2 diamonds. Both spades and diamond distribution is known. West has 7 vacant places and east has 7 too. But in clubs all little cards are known being the critical suit. East has 4 vacant places having followed to 3 clubs, 2 diamonds and 4 spades. While west has followed to 2D, 4S, and 2C and has 5 vacant places. Chances of west with 5:4 odds are in favour of holding queen of clubs which needs to be ruffed out. Equi partition in spades and diamonds favour probability break of 3-3 in clubs with percentage odds going up to 56%.
On an inference of an opening lead, vacant places can come in handy too knowing length and shortage immediately.
Suppose on Contract is 3NT West leads 2D
Diamonds side suit is known to be 4 with west and one with east on the opening lead. Now you have 3 hearts, 2 diamonds and need to have all 4 clubs to make 3NT. To find QC is essential. Vacant places tell you from side suit distribution that west has a 9 vacant places to east's 12 favouring east with QC 3:4
Suppose the opening lead was an honour card, KS in a 3NT contract.
You have 4 club tricks, 1 spade and need to have 4 diamond tricks to make the contract. Assuming west has 3 spades honours KQJ, he has 10 vacant places to east 13 favouring east to hold QD.
So winning second spade, you play a diamond to ace unblocking both clubs, all following east plays the last small diamond on the next round. All the little known cards in critical suit known west with 3 spades and 1 diamond with 9 vacant places to east's. 2 diamond, giving 11 vacant places with odds 9;11 in favour of east holding of QD, favouring the finesse.
But suppose with you as dealer, you opened 1C, N bids 1D, you had bid 1NT and N 3NT, again KS, lead connotes a different inference. Had west 5 spades to KQJ along with heart honour, he would have over called 1S. Therefore, with most of low spades being with east, the finesse position becomes dubious and favours the drop. In slams, such inferences, therefore, are less secure. Supposing instead of QH, you held AH.
Playing 6D, on lead of spade K, you can no longer rely on west holding the JS too along with QS as in a 3NT contract lead. Therefore, the vacant places are less reliable on such inferences. It is only when the distribution of a side suit is completely known or all the little cards of a critical suit that the theory of vacant places become the guiding light to give you the maximum odds of success in the location of the key card required for the making of your contract. This concludes the 3 part series on the theory of vacant places in Bridge hoping you are now better equipped to find the winning key cards on the best odds.

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North       South
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 KQ73           6
    Q        A984
  KQ6     AJ10943
AKJ102         75
=================

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North       South
=================
  764         A10
  J73        Q106
AJ943       K1082
   AQ        KJ94
=================

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With bidding:
================
North      South
================
   1C         1D
   2S         3H
  4NT         5H
   6D   ALL PASS
================

================
North      South
================
   94       Q105
  KQ5         A2
 A763       K954
KJ105       A962
================

================
North      South
================
  763        A10
  J73       A106
AJ943      K1082
   AQ       KJ94
================