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

hey everyone, i've been thinking about application performance lately and wanted to start a discussion on Content Delivery Networks. we all know they can help speed things up by caching assets closer to users. but when do you actually *need* one? is it purely based on traffic volume, or are there specific types of content or user distribution patterns that make a CDN a no-brainer? curious to hear about your experiences and decision-making processes