Serving N images all cropped slightly differently isn't going to save bandwidth over serving an image one time, caching it, and then doing slightly different cropping in the browser.

Airbnb's homepage images only seem to be 50-90KB per image. And they already do some image resizing:

https://a0.muscache.com/im/pictures/prohost-api/Hosting-4850...

vs.

https://a0.muscache.com/im/pictures/prohost-api/Hosting-4850...

If you compare the slightly cropped homepage images to their uncropped versions, you just aren't saving a bunch of bandwidth by serving static crops, especially since you need new crops once the user clicks in to property pages.

Finally, images (1.3MB) only account for 10% of airbnb's homepage transfer in desktop Chrome (13MB total) and 2% in desktop Safari (60MB total... content blocker bug?). Images seem to be the least of their worries.