I have taken minor hull and module damage while out in the black, though only from jumping in between multiple stars, and cooking a bit in the time it took to get away. The AFMU fixed the module damage, and given that I regularly use Neutron Boosts, I need the AFMU to keep[ my FSD in good shape. That said, I am not really seeing the value of repair limpets. Presumably, if ones hull is dangerously close to failure and in imminent need of repair, the power plant is in bad shape too...