The offensive and defensive value of the cards is in direct relation to how you are appraising your hand. You can immediately tell when you appraise your hand whether or not you need to take the offensive or defensive play against your opponent.
With exception of actual melds, the offensive characteristics of a hand are developed by the number of opportunities that are afforded to you with any combination of two or more cards. A combination such as a King and Queen, or an Ace and Two offers only one way to complete a meld. A combination of two Kings or two 7’s offers two offensive possibilities, as does a 7 ♦ 8 ♦ combination. However if you have a 3 ♣ 5 ♣, it again only offers one possibility.
The run combination is considered slightly more valuable than two pair because once a third card is added for the meld, the run combination will now offer two ways to obtain the fourth card whereas a meld of three Kings for example will offer only one fourth-card possibility.
You want to keep cards that give you offensive value for the most part. That would include cards such as 7 ♦, 8 ♦, and the 7 ♥. That yields a four-way melding opportunity, but it also gives you the possibility of more if you can add the 8 ♥ to this mix. That automatically doubles your melding possibilities. Two-way melding combinations should be played for the sole purpose of increasing them to at least four-way combinations at every opportunity. A further advantage to the offensive values of these cards is that it effectively ties up your opponents hand to the largest possible extent if he is playing a defensive game.
While the odds of developing the fourth card in a meld are twice as good when you have a run rather than a three of a kind meld, it works to the reverse if you are playing defensively. A meld such as three 10’s allows a defensive player to lay off only one card on that run. A meld such as 7 ♦, 8 ♦, and 9 ♦ permits a defensive player to lay off as many as four cards. An example of this is if you were holding that hand and he was holding a 5 ♦, 6 ♦, 10 ♦, and a J ♦. He could lay off all the cards and either underknock or call a gin off. Thus, when playing that type of hand you definitely want to knock, and when playing against a defensive type of player, it is best to hold three of a kind melds rather than suit sequences.
The strategy of play depends largely on the type of player your opponent is, but it is equally as important to know what offensive and defensive value a particular meld or run has so that you can use it to your advantage.