Exported sprites and textures are grouped together in larger spritesheets to save memory. They're packed in power-of-two square image sizes (i.e. 128x128, 256x256 etc.) because that's how many systems store and process images. This means that a spritesheet could have a large empty space, which might appear inefficient, but in actuality it would be more memory efficient than keeping the sprites separate.
Unless you're using a lot of ENORMOUS sprites or particular custom GL effects, it shouldn't cause any issues.