When should you actually use a CDN?

i've been thinking about how to best serve static assets like images and JS files to a global user base. we're starting to see slow load times in regions far from our origin server. a Content Delivery Network (CDN) seems like the obvious solution, but i'm curious about the tipping point. at what point does the complexity and cost of setting up and managing a CDN become more beneficial than just sticking with our current single-region hosting for static content