Although all that has been said it true, there is a lot to consider in this question.
* The safety will line up as the deepest defender no matter what your defensive settings, so it will take him several steps before he reaches the LOS.
* If you are worried about the run then taking a safety away, your best open field tackler, could open a hole in your 3rd level run defense.
* Your CB will line up on the LOS
* If the offense you are defending against only utilizes one WR then you have a CB that is free.
* If you are defending an Offense with no more than three receivers in pass patterns then when you move a LB to "line" then a CB or a Safety will take his pass coverage responsibilities and in effect become like another LB.
* You can shorten the setting for what is considered "Long" in your defensive playbook to move your safeties closer to the LOS, but be careful because their reaction time and tackling angles change and you can more easily give up big plays.