There are two opposite views on whether or not slicing Web graphics actually makes them load faster. Some people say that image slicing does not reduce the overall size of image and faster loading is just a subjective perception. Others say that slicing can actually increase load speed due to the additional simultaneous requests to the Web server.
Actually, there is some truth in both of these arguments. Usually, simple slicing does not reduce image size and even may decrease the load speed. But you can greatly reduce overall image size and speed up loading by optimizing the image. Furthermore you can make your images look better with the lesser size. The key is optimizing of each slice separately, using the most optimal compressing format for each of them.
Some parts of your image will be compressed better using JPEG algorithm, some parts will be compressed better using GIF or PNG. Replace the solid colored areas of your image with a "No Image" slice (empty table cell of the same color) and you get the same look image lesser in size.
In additional, image slicing is essential instrument for creating the complex graphics (menus, page layouts, buttons, rollover effects and so on).
Some examples of image slicing is described in details below.
Example 1 - how to create rollovers
Example 2 - how to optimize complex image
Example 3 - how to create site menu (coming soon)
Example 4 - how to create bordered page (coming soon)