The biggest use case of open-source LLM is that your use of it is private and input is not sent to third-parties. For a personal perspective, it means it's free and accessible forever (and yes can be used for NSFW stuff), and from a business perspective, it matters both for legal reasons such as finetuning on propritary data and it mitigates the business liability of issues with the third-party LLM provider such as random API outages.