As with all things in poker, there needs to be a reason.
When we open, there's a reason.
When we 3-bet, there's a reason.
When we decide to check-raise the turn, there's a reason.
So, if we decide to show our cards, there needs to be a reason. We don't just show cards for the sake of showing cards.
In general you shouldn't be showing your cards. But an experienced player knows when he can and there's really only two reasons why:
1. To represent a playing style that's the opposite of how you're actually playing
2. To represent a playing style that's the opposite of how you will be playing future hands.
Let's say you're playing with a loose, wide range of cards. You've been in several pots and won a few of them without having to show down any of your hands.
From your opponents perspective, you're a loose player. You're in a lot of pots and winning them. It looks like your stealing and bullying the table around.
But then you pick up KK. After you win the pot, you show your KK to make people think that you're actually only playing with good cards. A couple hands later, you show AQ.
So now, everyone's perspective of how you play has changed. They thought you were loose, but now you've shown tight cards. In future hands, they will tend to think you're only playing with strong hands.
This is actually a very old technique that goes back to the earliest days of poker. You play weak hands, but only show down the strong ones. It reduces your image as a loose player and allows you to win pots by representing a strong hand when you don't actually have one. People will remember the big cards you showed.
Now let's say you've been playing loose for an hour of so and won a few pots. You've decided it's time to tighten things up a bit because the blinds have gone up a few levels and you're getting near the bubble.
You just won a pot with a huge bluff. So, you can show the table the lousy cards you won with and then immediately switch your style to conservative play. People will have the impression you're a loose, aggressive players, but you're no longer playing that way.
This makes it easier for you to induce action when you have strong cards. You're raises won't be taken seriously. You'll get the calls and 3-bets you're looking for when the
equity of your hand is strong. Your table image of being loose is still in their minds, but this assumption works against them because they play into your hand just the way you want them to.