Does it benefit AEW to work with Impact?

Only to the extent that we as Fans get to see Wrestlers wrestle who otherwise wouldn't. It raises the profile of Impact for Wrestling Fans who may not have paid much attention to Impact (Total Non-Stop Action) Wrestling over the last 19 Years. Moreover we've seen Wrestlers who have been working for The NWA, New Japan Pro Wrestling, Major League Wrestling and other Professional Wrestling Promotions, so I as someone who has always been interested in following a number of Professional Wrestling Promotions there are possibilities again of matches that you could not hoped to have seen even a year ago.

So far the Impact relationship has allowed a Bullet Club reunion and the constantly annoying-in-the-right-way presence of Don Callis on television.  For that alone, it's been a worthwhile endeavor to team up with Impact.  I also have a feeling that relations with AAA and Impact will allow Omega to continue his belt collector gimmick.  Who knows? maybe he'll take the NWA strap off of Aldis. Powerrr certainly seems to be teasing a defense against outside talent, and my god does Aldis ever need a legitimate challenger for that belt.

Back to the topic at hand though, exposure on another media outlet is a good thing, even if the media outlet is Twitch and drawing far fewer eyes than the AEW product.A new fan is a new fan, and I don't think any company would turn their nose up to attracting any number of new viewers, even if that number is one.

It gives journalists something to write about, and fans something to drool over. Until the moment when someone goes rogue, this benefits everyone.

it might benefit them