when should a small app bother with a cdn, really

hey folks, ive been thinkin about performance optomization for a relitively small web app were buildin. its not high traffic yet, but we wanna make sure its snappy. were considerin usin a CDN to cache static assets like images and CSS. for a small-scale project, does anyone have experience with CDNs where the cost-to-benefit ratio was questionable? are there specific thresholds of traffic or asset size where it starts makin undeniable sense, or are there smarter caching strategies for smaller apps before jumpin to a full CDN