What does slots actually do?

Think about it, youre in the middle of a boss fight, and you turn to your companion Stezer/Tifa/Cait Sith/Wakka. "HEY WE NEED YOU TO PULL OFF THAT SUPER POWERFUL MOVE YOU DID LAST TIME AND FINISH THIS GUY OFF!"

"Sure thing buddy! Just a sec"

He/she/it then proceeds to pull a slot machine out of thin air and goes a round.

Oh darn! seems I've made two hits and a miss. The slot machine then returns to pocket space and your pal decides to summon a bunny or play a friendly game of catch with the enemy or something.

What the hell dude!?

The enemy then proceeds to breath fire on you and you all fall down

Man I hated slots...

Cloud: "Go Cait! Use your limit break!"
Cait Sith: "Sure thing, buddy! Go Slots!"

*uses limit break*

Cait Sith: "Oh no."
Cloud: "What's wrong?"
Cait Sith: "I think I've just killed us all."
Cloud: "What? What do you mean?"
Cait Sith: "This slot combination erm... it err... kills all of us."
Cloud: "WHAT?!! Jesus titty-smurfing Christ man. No wonder everyone hates you, you f..."

~ GAME OVER ~

Slots in the case of Tifa and Wakka are simply a mechanic for the player. It determines how their attacks work. Slots in the case of Cait Sith and Setzer are completely different in that the actual slot machine is the attack and the effect is reliant on that. As for how it makes any smurfing sense.... It doesn't, I guess.

It still makes no sense in the case of Wakka.
Tidus needs to get his timing right, auron needs to perform a specific action to do his limit, lulu has to charge up her energy, rikku mixes two things together, are we to believe that Wakka needs to kick the ball in the right spot at the right time or it turns into fire?

He also needs to focus and ensure that he hits the right spots. If his timing is a little off he won't hit as frequently though it might still work. In the case of Attack Reels, at least; I never used the others. Wakka's Overdrive is similar to the final phase of a discus throw. If you release at the wrong time you will not hit maximum distance.

Wakka's smurfing useless.