when to use a cdn for static assets

hey everyone, i've been thinking about static asset delivery lately, especially for web apps. we all know cdns are great for performance, but when does it actually make sense to add one to the architecture? is it only for high-traffic sites, or are there other things like where users are located, just how many assets you have, or even just making cache management easier that make a cdn a good choice for smaller projects too? what's your experience with this