Actually, "worst case" would be you drop it twice, and need two replacements at $249 ($498 total) vs. two replacements at $49 and the $100 AC+ cost ($200 total). Or maybe "worst case" is that that battery (or display, or home button, or sleep switch) just stops working during the second year, when AC+ has extended the factory warranty a second year, so you get a FREE replacement vs the $249 replacement fee an unlimited number of times for the $100 AC+ cost. And if you live far from an Apple store, AC+ provides "express replacement", which can be a big convenience.
But it is still an "extended warranty" and accidental damage "insurance" which companies sell as, in the aggregate, they make a profit doing so -- only because (in the aggregate) most consumers do not ever need or profit from them. It is a personal decision, though, because there is value in many cases.