Many of the effects of clientside script can be accomplished on the server
Many of the effects of serverside script can be accomplished on the client
the best design choices choose horses for courses
Server side, the page is smaller when sent to the browser = faster
client side, essentially trivial things dont tie up the server
anything to do with security, is generally better on the server(1), client side validation is a joke
but clientside scripts to point the user to irrational input data, something completely out of the park, is faster than submitting the page and getting the server response back.