when's the best time to start using a cdn

Hey everyone, I've been thinking a lot about how we serve static assets and external APIs efficiently, especially as traffic grows. We're currently serving everything directly from our app servers and seeing some pretty high latency in certain regions. I know CDNs are a common solution, but I'm curious about the specific triggers that make it the right move. Is it purely based on traffic volume, geographical distribution, or are there other factors like cost savings or offloading server load that should play a bigger role? What have been your experiences?