[Suicide Junkie]

According to my calcluations, it turned out that for unmodded SE4, if your ship could be expected to survive 7 or more turns in combat after first being hit, then adding a regenerator would provide more protection than adding a shield generator instead.

So, unmodded regenerators are really only useful for small fleets or one-on-one fights, and/or for races with a significant To-Hit defense advantage