[Seaside] Component tree vs. DOM tree

[itsme213]

Seaside currently keeps a server-side component tree. Each component will 
typically render a sub-tree of the browser-side DOM tree.

What would be the disadvantage of maintaining a unified server-side DOM 
tree, where some (but not all) nodes would correspond to full-blown Seaside 
components? I think Michael Lucas-Smith had mentioned this

"you tend to want only one tree to represent your UI state on the server, 
not two - instead of having WAComponent and WABrush separated, we combined 
the two so that each widget was an element which was also represented on the 
client side as a DOM node."

Thanks - Sophie