A Java UI runs as a native application on your client system. It looks and feels just like any of your other applications. Compared with a purely browser based UI, the experience is much richer. If you have ever tried to enter a lot of transactions through a web browser interface , you will know just how tedious that can be.
The Java UI is updated automatically, if necessary, when you login. It is delivered over the net, so you have no local configurations to manage. Because it runs on so many platforms, in general you can run it on any old PC you have to hand. So it is cost effective technology too.