There are a few useful additions that have been added to the client API around the Save event. They are 3 methods that have been formally introduced:

getSaveMode: Returns a value indicating how the save event was initiated by the user.
isDefaultPrevented: Returns a value indicating whether the save event has been canceled because the preventDefault method was used in this event hander or a previous event handler.
preventDefault: Cancels the save operation, but all remaining handlers for the event will still be executed.

The key method is the getSaveMode function. Think about the new auto-save feature on updated forms. The getSaveMode function allow the javascript method executing on the Save event to know why/how the record is being saved. That gives you the flexibility as a developer to add some additional logic to handle your scenario… Below is the list of values returned by the getSaveMode function based on the entity type.

This is fantastic as you can now write script to handle very specific scenario like an activity being resolved, a record being saved and closed, assigned and other cases. Below is a usage example in which we prevent the auto-save from happening as presented in the SDK documentation:

function preventAutoSave(econtext) {
   var eventArgs = econtext.getEventArgs();
   if (eventArgs.getSaveMode() == 70) {
      eventArgs.preventDefault();
   }
}

Cheers