Board Thread:Plants vs. Zombies 2/@comment-1764483-20150625125327/@comment-7234182-20150702224002

By the way, if you are wondering why they bother doing this when they could just have the largest one in, then the simple explanation is performance.

Mobile devices are pretty underpowered (compared to desktop computers), and scaling an image is wasting precious processing time that could be used elsewhere. To mitigate this, they pack various textures already scaled to different sizes. Then depending on the resolution of your device, a texture of the appropriate size is chosen. When the game renders it only has to worry about loading the texture and displaying it on screen, and not resizing it.