usability – What is the purpose of a swap button in an airline booking app?

It’s to save the user time from having to re-input values.

I’ve heard it called a swap button, but that’s informal.

This is a common pattern in applications where a trip is being planned (or en route). It allows users to quickly reverse the start and end destinations.

enter image description here

The principle behind it is more important to know: don’t make users do more work than they need to.