[dspillett]

While it can lower server load (though I doubt significantly in most cases) and bandwidth use (in some cases, where more data is present than the template chooses to display, it can increase bandwidth needed - but that is usually a design/tradeoff issue elsewhere), the main reason for pushing more to the client is UI responsiveness.

A lot of stuff is being pushed to the client now to reduce the amount of crosstalk between client and server, so things feel snappier for the user, with the goal to be to talk to the server when absolutely required (i.e. to save data or application state, to request new data or check the data the client has is up-to-date, or when some of your business logic needs to make a decision the client-side can't be trusted with).

If you are making display decisions client-side then your template engine probably needs to be client-side.