When playing canasta, why would I ever want to discard a wild card rather than adding it to a meld?
The main reason is to freeze the discard pile so that you have more safe choices to discard after that.
Often in Canasta, winning vs losing comes down to who gets to pick up the discard pile. When the discard pile gets big enough, the person who eventually gets to pick it up can score huge amounts of points by melding everything in it.
Discarding a wild card helps prevent this in 2 ways:

It is a guaranteed &quot;safe&quot; discard that cannot be picked up, the same as a black &quot;3&quot;.

It freezes the discard pile, which means that cards you discard after that cannot allow your opponent to pick up the discard pile unless they have two matching naturals in their hand. This means that you can generally safely discard cards that they already have melded. Of course your opponent could have 3 of a kind melded and still have two more in their hand, but your odds are better. It can also give you several guaranteed safe discards; for example if your opponent has melded four &quot;6&quot;s, and you are holding three &quot;6&quot;s in your hand, then discarding a wild card allows you to discard those &quot;6&quot;s over the next three turns without any risk of your opponent picking up the discard pile.


Note that this does have the same effect against you as well; so it is better for you if you have more cards in hand than your opponent, or fewer things melded.