[Suicide Junkie]

Shields use CA ability, rather than sheer hitpoints.
Thus, they absorb 20/33/50/66/80 percent of the damage depending on damage type. (Maximum... large shots can overwhelm it)

Leaky armor is just non-armor components with lots of hitpoints so they are often, but not always hit first.
With lots of them, you reduce the rate of loss of your critical components like engines weapons and lifesupport.