From User prospective:
– Rich interface.
– Easy to use and/or learn to use.
– Much information on single page (accordion layout, collapsible panel, and so forth).
– Consistent look and feel.
– Drag and Drop facility, etc.
From Developer prospective:
– Declarative way of building application.
– 150+ ready to use Rich component.
– Multiply ways to develop and reuse components (declarative component, page template, taskflows, etc.)
– Highly decoupled
– SOA enable, And so forth.