A first-time visitor to your page may have to make several HTTP requests, but by using the Expires header you make those components cacheable.
This avoids unnecessary HTTP requests on subsequent page views.
A web server uses the Expires header in the HTTP response to tell the client how long a component can be cached.
Most of this time is tied up in downloading all the components in the page: images, stylesheets, scripts, Flash, etc.Inline images use the URL scheme to embed the image data in the actual page. Combining inline images into your (cached) stylesheets is a way to reduce HTTP requests and avoid increasing the size of your pages.Inline images are not yet supported across all major browsers.Defining the coordinates of image maps can be tedious and error prone.Using image maps for navigation is not accessible too, so it's not recommended.