If a custom build doesn't need manually triggered events, it could save a bunch of bytes by removing jQuery.event.trigger(), jQuery.event.simulate(), jQuery.fn.trigger(), and jQuery.fn.triggerHandler(). This would mostly be useful for the 2.x (now 3.x-master) branch because the 1.x (3.x-compat) branch relies pretty heavily on manually triggered events to fix up IE8. On master, manual triggering is used to create bubbling focusin/out events and fire ajax events, but there are other approaches devs can use for both situations.