They slow down the downloading. Most of these pictures likely aren't worth the wait. Think twice about every single picture on the page and what purpose it serves. Make sure each image is as compressed and small as possible which probably means finding some professional help. Graphics must be optimized for proper Web display and this usually requires image editing software.
Pictures are important.
They can enhance your site. Currently, many sites do not utilize ALT even though it has been a part of HTML since the beginning. Try to minimize the number of pictures and their sizes on the home page of your site. You want to grab the visitor's attention immediately with the home page and forcing them to wait for the 100K image of your corporate headquarters to download doesn't succeed at this very well. Linking from the home page to an image of the headquarters is much wiser.