More Capable Mapping Software
The ArcIMS Java Viewer has far many more options than the HTML version. For example, it will actually download the features as vector layers not just images. This gives you more robust selecting options, buffering tools, and allows you to edit the features. Because this system is so powerful, it has not been able to run successfully on all platforms. Thus if you run into a problem using the Java pages you will need to use the HTML Viewer.