What it does
Quick Attack is a Normal-type physical move with priority +1. The base power isn't impressive, but that's not the point. You use it because you need to go first regardless of Speed — specifically, when the opposing Pokémon is low enough on HP to KO but would otherwise outspeed you and potentially take you out first.
In doubles, Quick Attack hits one target only, at full damage (no doubles spread penalty). The priority guarantee works against any Speed value — there's no opponent fast enough that they outrun a +1 move with a 0 move. Where it gets tricky is if both players are using priority moves, in which case Speed is the tiebreaker.
A practical edge case: the opponent's Pokémon has a Focus Sash and survives at 1 HP. Without priority, it might hit you first. Quick Attack circumvents that, cleanly finishing the job before it can respond.
Who runs it
Flareon at 84% adoption has it essentially as a staple. Speed 65 is not going to win many natural speed tiebreaks, so Quick Attack is the insurance policy — an always-available way to clean up weakened targets that would otherwise retaliate first.
Sylveon runs it at 69%. Primary Special Attack Fairy-type, Speed 65. Same logic as Flareon: without priority, low-HP targets can flip the damage order on you. Quick Attack closes those gaps.
Diggersby is a different case. With Huge Power, its physical Attack is enormous, which means even a low base power move like Quick Attack deals real damage. Speed 78 is middling, and priority fill-in is useful in speed-contested situations.
How to use it
Simple rule: use Quick Attack when the target is low enough to KO and would otherwise go first and threaten your Pokémon. If the target's not low, you're giving up a higher-damage move for priority you don't need.
In doubles, before committing to Quick Attack, check whether removing that Pokémon changes the math for your partner. Sometimes KOing one side early lets your other Pokémon double-target the remaining threat, which is more efficient than splitting attacks.
Watch the priority brackets. If the opponent also has a priority move queued, your Quick Attack and their priority move both land in the same bracket — Speed decides first.
Tips & strategy
The most common misuse: clicking Quick Attack on a Pokémon that's at 40% HP, wasting the priority bracket on something that doesn't need it and dealing less damage than a real attack would. Priority is valuable because it prevents being KO'd first — it has no extra damage upside. Use it when that specific tradeoff is worth it.
Ghost-types are completely immune to Normal-type moves. Quick Attack deals zero damage to a Ghost-type target. If the low-HP target is a Ghost, you need a different plan.
Under Trick Room, Speed order reverses but priority brackets don't. Quick Attack is still +1 and still goes first — the Trick Room doesn't flip that. Worth remembering if you're running against a Trick Room team that also happens to have a Quick Attack user.