When should you think about using a CDN for your app?

hey folks, ive been thinking a lot about performance lately, especially for web apps serving geographically distributed users. we're currently handling static assets on our own servers, but its starting to feel like a bottleneck. at what point do you typically start evaluating a Content Delivery Network (CDN)? are there specific metrics or traffic patterns that signal its time to look into one, or is it more of a proactive decision? what are your experiences with CDNs?