when should you introduce a cdn, its prob when youre website is getting a lot of traffic and you need to speed things

hey everyone, i've been thinking a lot about content delivery lately. we've got a growing user base, and i'm starting to wonder when a Content Delivery Network (CDN) goes from being a 'nice to have' to a 'must-have' for an application. our latency is starting to creep up for users further away from our main servers. what are your experiences? at what point did you find a CDN essential for performance or cost savings, and any specific metrics you look at before making the jump