Originally Posted by FriendlyPilot

Imagine you are a Trueblue award traveler and you need to fly to Boise, Memphis, Pensacola, St Louis, San Antonio, Minneapolis, or one of about 30 cities Jetblue does not fly to that Spirit does. Currently there is no advantage of flying to those cities on United, other than if you want a premium seat and would likely fly on Spirit because of the lower fare.

Now imagine that instead of even looking to see if Spirit, Delta, American, Frontier, etc flies there, you just check the Jetblue app and see that you can get a flight on United either direct or 1 connection and continue to not only build status and perks on Jetblue but also now United. Miles and benefits that can get you free trips to Europe, Hawaii, Asia etc. So instead of buying tickets on Delta to Rome, you fly on United out of EWR because you have status now that you didn't have before.