Active-Active vs Active-Passive
Whether all regions serve traffic simultaneously, or one serves while another waits to take over — a choice about which failure mode you would rather have.
Active-passive runs a standby region that receives replicated data but no traffic. Failover is an explicit action. Simpler, because there is exactly one place writes happen, so there are no conflicts. The costs are that the standby is paid for and idle, and — the significant one — the failover path is rarely exercised, so its true RTO is unknown until the day it matters.
Active-active serves from all regions. Better latency for a distributed user base, capacity used rather than idle, and the failover path is exercised continuously because it is the normal path. The cost is that writes happen in more than one place, which forces a decision about conflicts and about what happens during a partition.
The design that avoids most of active-active's difficulty is partitioned active-active: every region serves traffic, but each record has a home region that owns its writes. Users are homed; cross-region writes are a rare forwarded path. That gives the latency and utilisation benefits without global write conflicts, and it is what most large multi-region systems actually run.
The question that decides it is not ambition but RTO, RPO and residency. Active-passive with a tested failover satisfies most requirements at much lower complexity, and "we should be active-active" without those numbers is a preference rather than a design.