It alos makes my server software conceptually simpler - which is always nice
This has gigantic performance increases for servers under heavy load, and it puts the display logic in a domain that is more naturally suited to dealing with it (JavaScript and the DOM instead of treating HTML as just a string).
The pattern also promotes the use of RESTful APIs for data access from the server, which has the wonderful bonus of allowing you to make your data publicly accessible for free if you want to.
My client side user should know nothing about Dbase lookups or persona verification - just as server model should not care about displaying addresses. Overall I think getting the crap out of the server makes it much much easier to reason and architect