Well... It kinda is a bad idea to drop live ordinance over friendly territory. :P If you happen to be jumped when on your way to target (like often happens if you fly online) and have a couple MRM's in MPRF mode coming at you, sometimes you need to do a split S and get outta dodge fast! So, yeah, umm, jettisoning makes a lot of sense.
However, you might not care if your bombs hit some unsuspecting persons house. I do.