The file is also large for photographic images. GIF is still the smallest file for 16 or 256 color data like graphic art or screen captures or 2 color Line art, and is the format of choice for that kind of graphic images. Simple images like a company logo should be reduced to 16 colors if possible and saved as a GIF for smallest size on the web. Some image programs will convert to any number of colors, and a complex logo might look bad at 16 colors, but look very good at say 43 colors. The fewer colors, the smaller the GIF file.
Size is important to web pages.
But GIF files will be smaller for graphic artwork. GIF also optionally offers transparent backgrounds. When you select GIF format, your FILE - SAVE AS dialog box has an Option Button. Under that Option button is an option for transparency, to specify which one GIF palette index is to be transparent. Also, you will not even be offered the GIF format as a choice until you have reduced the image to 256 colors or less.