It lets you change reverse proxy or run a website with TLS completely independently of the certbot. The certbot deals with obtaining certs and leaves them in a dir, and the proxies or webservers just take them from that dir. If the proxy container breaks the certbot still does its thing etc.
It also makes it easier to do stuff like run different proxies in paralel for different things, chain proxies (for instance if you need to use a VPS because you can’t forward ports) and so on.
But it’s all for advanced setups, for basic stuff I’d still go with NPM.