Losing data or any kind of outage is unacceptable and intolerable: especially for mission-critical systems which have to beat tough SLAs.
High availability, fault tolerance, and disaster recovery are the essentials for mission-critical services. You might consider adopting cross-region replication if you are managing a service in one of following domains: monitoring, security, IT management, finance, e-commerce, telecommunications, health services, control systems, etc. In such systems, an outage for a few hours could mean a very substantial loss of revenue, and thus, an urgent need to handle crisis situations.
Data loss in case of failures is not an option anymore.