Any form of status by itself is very crippling in Doubles, whether it be Thunder Wave or Swagger. In Singles, you could use smart switching and pure type advantage to overcome status disadvantages, but doing so in Doubles is much riskier due to the doubled opposing offensive pressure. If one of your Pokemon is temporarily stunned by parahax or confusion, the tide is turned to two against one, giving your opponent a lot of momentum and offensive power. For this reason, things like Thundurus-I or Sableye are intensely annoying yet useful because of their ability to spread such crippling attacks with almost guaranteed reliability from Prankster. (like honestly I could simply just spam TWave with a thundy and not even be any worse off)
Swagger is just about as bad (or good if you're Satan) as everyone claims it to be. While theoretically the percentage chance that it does anything might be undesirable, it is a relatively risk free weapon to carry out in the field. In the long run, it has every bit of potential that attacks like Draco Meteor have to wreak havoc, simply because of its ability to stun and deal damage at the same time, indefinitely. In Singles, it's an annoyance. In Doubles, it's literally like permanent Fake Out spam so long as you're lucky enough (or unlucky enough if you're in the receiving end.) Think of it this way- using Nyttyn's numbers, Swagger has a 45% chance of not only stunning your opponent, but also dealing damage, and sometimes decent damage too, especially since it also applies a x2 opposing Attack boost to fuel the self-smack power. It's like a Fake Out that has a 45% chance to work (which is still very decent), and when it does, deals a shitton of damage depending on the opponent. as I said earlier, in those turns where the confused Pokemon hits itself, the field turns into two against one, and the opposing side immediately gains the chance to almost freely deal significant damage. And that's not just for the first turn; the chances rise to 50% until the confusion wears out. If both of your Pokemon are confused, only 25% of the time will both of them move, which is half the chance of one of them being stunned, and the same chance as neither of them moving.
Think about it. Two confused Pokemon, and 25% of the time, neither of them move, basically giving both of your opponent's Pokemon free attacks.
If you're worried about the attack boost being used against you; well, the numbers are just as much for you as they are against you. (except, not really) The amount of damage you'll take will not increase, because your opponent will only be (theoretically) attacking you 50% of the time, which neutralizes the x2 attack boost. And that's only if your opponent is a physical attacker; if they're a special attacker, it's even better for you, as their damage output will be effectively halved due to the fact that Swagger boosts their other offensive stat.
So... when again is it not worth it?
