Swingy Combat: Any combat in which the participants put all of their armor and weapons into a bowl, then draw out the same at random and pair off to fight.
That could happen in a non-swingy combat, too. The results are simply not as dramatic. The point is that in a swingy combat, most ideal tactics involve minimizing random, uncontrolled events.
And how does that exactly work on the dice rolling aspect? That's the part I'm questioning.
Now the death ward thing that another poster mentioned to cancel the death abilities, that to me isn't 'swingy' combat. That's being prepared for a potentially huge fight and praying that they don't successfully dispel your magic (which I believe Pathfinder put the nerf on.)
Hmm. I must be doing something wrong, then, because that's exactly how Sleep was in the last 3e campaign I played in where it saw any use. We were a party of elves (with typical high Dex and low Str), and it was only when our melee types were getting totally pwned by hulking brutes that our wizard would break out the Sleep. Several times, it was the only reason we survived.
And that campaign is typical of my 3e experiences.
There are even assumptions that spellcasters should have every buff, ever, on the entire party, including multiple flavors of Resist Energy, Overland Flight, Greater Magic Weapon, etc.
While I would argue that the the Death Ward aspect is a very minor portion of "swingyness rewards tactics", it can be used to illustrate the point. The *reward or penalty* of good/bad tactics is much larger in swingy combat.
Carefully maneuvering to rob an elite of a round's worth of attacks in 4e? Valuable, to be sure, but unlikely to have a large effect. Carefully maneuvering to restrict the BBEG Giant of a Full Attack opportunity (still leaving him with a single attack!) in 3e? A matter of life and death. The value of modifying a single event goes down as the number of events goes up. Swingy combats have fewer events, and so the value of good tactics goes up.
In the rocket-tag limit of swingyness, the only defense you have in using tactics to get the first attack, and the value of good tactics is nigh infinite. (and you are guaranteed an early TPK, these aren't mutually exclusive)
How so? The combat rewards of good planning can be completely neutralized by bad roles on the party's side and good roles on the enemy's side. Where is the reward?
Its also the factor that swingy combats are more dangerous, so groups have more incentive to plan..