from my point of view, if you have allowed the lens to go into such a situation where the filter might be of actual help - you obviously don't take good care of your equipment. i can hardly recall any situation where i even came close to compromising the safety of my equipment.
once again, i stress that a filter is of limited use in protecting the lens. the previous replier has stated that the filter took the impact and broke into 3 pieces, etc - similarly there have also been instances where people have claimed that the filter broke, and scratched their lens. you have to remember that the filter is only applicable for protecting the front element - if the lens lands on the side, on the rear, this offers no help at all. it can be a double-edged sword.
frankly speaking, if you think it will help, you can buy it.
from my point of view however, it seems to be a psychological thing - pay $x for protection, and the lens will be protected. the truth is that you are paying $x for increased peace of mind, while fooling yourself that the lens is somehow magically immune to drops as a result of this. might as well use the money to buy insurance for the lens, if that is your objective.