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

Complementing what Sulthan said:

Because you didn't propitiated proper images for a specific device, it has to downscale or upscale. These processes will use up your memory and processing, resulting maybe in a decrease of performance, depending on how many images at a time you're doing it and the size of image.