just because .gif supports animation doesn't mean that that's all it's good for.
.gif is the preferred format for images with less than 256 colors, or images with large (especially horizontal) swatches of color because the RLE encoding scheme can squeeze 2,000 white pixels into the same number of bytes (pretty much) as 3 white pixels.
In addition, .gif is a lossless compression scheme, which means that none of the original image data is lost. with .jpg, you get dithering and color loss unless you save at the highest quality.
so in short, photos use .jpg, cartoons/line art/simple images use .gif