When should you really consider CQRS?

I've been mulling over Command Query Responsibility Segregation (CQRS) lately. The core concept, splitting up read and write models, makes sense. But when does it *really* become a must-have pattern, you know? It's often suggested for super complicated areas, but are there simpler signs? I'd love to hear about what makes you guys decide to dive into CQRS instead of just keeping a single, unified model.