There are several scenarios when it is useful. For instance, avios bookings can be changed, but there is a fee, so it is often cheaper to cancel them (your avios are refunded and you only lose the fees you paid if they are less than the cancellation fee) and make a new reservation. However, if you cancel the whole booking just to change, say, the outbound, you may find out that there are no available seats to rebook the same inbound you had (your cancelled award seat does not necessarily go back to the redemption bucket).


We are talking about outbound and inbound flights on separate days (i.e., at both ends of a vacation), not about connecting flights on the same day, so there should not be any danger.

In any case, by the way, AA protects OW connections on separate tickets (useful, for instance, if you want to connect from an award segment to a paid one).