Why do I need @1x, @2x and @3x iOS images?

Question

Why do we need these 3 particular image types?

If I have a button on my app with a background image say, 50 pixels x 50 pixels, why do I need 3 versions of this imag

Answer 1

It is because if you provide one high resolution graphic it would be waste of space on a users' device. Thanks to app slicing the device will download (from App Store) only the parts that actually fits the device (so retina device won't download non retina graphics). This is why Apple created assets catalogs and this kind of rules to follow. They describe it in their sessions.

In short it is to decrease memory/disk usage so it is all about increasing performance and user experience