When should you switch from one database to replication?

hey folks, im working on scaling a growing web application and we're starting to feel the strain on our single database instance. We're hitting limits on read throughput and occasionally seeing performance dips during peak hours. We've discussed potentially moving to a primary-replica setup, but im curious about what triggers this decision for most teams. Are there specific metrics you look at? Do you wait until you hit hard limits, or do you proactively plan for replication when you anticipate growth? What were your experiences and what challenges did you face when implementing replication for the first time?