An example of a "graphic" image:

An original 8 bit indexed image - file size, 8KB

Color map cut down to 6 bit (64 colors) with no significant loss of quality. Any further reduction resulted in a couple of the solid color fields dithering badly. File size, 6KB

Here's the same image as a JPG. Notice the compression artifacts in the solid color circles and around the black letters. (See enlarged area) File size, 12KB!