when should you start thinking about database replication?

So, I've been running some services lately, and our single database is starting to really slow things down. It's becoming a bottleneck for reading data, and honestly, I'm worried about it being a single point of failure too. I'm wondering when you all usually decide it's time to add read replicas or set up master-slave replication. Do you wait until the load gets too high, or do things like disaster recovery planning make you do it earlier? What was your experience like?