Ideally you want to grease before it squeeks.If you wait until it is squeeking you have metal on metal contact somewhere in the hinge.That kind of contact results in hinge wear.As a side note an unlubricated hinge requires more effort to close the door and that can resultin broken armrests or door pulls.I generally lube the drivers door every other oil change and the other doors, hood and trunk once a year. (mechanics.stackexchange.com)