I'm using local LLMs for battle-testing an app by impersonating various personae with bad intentions (mostly on the social side, but also ones trying to break the system). Off-the-shelf cloud LLMs refuse such things (probably rightfully so); Llama 3.3 in q8, and qwen 2.5 72b even more so, are surprisingly good for this.

Also, even not-so-capable, smallish LLMs are able to be really good testers even outside the bad persona domain (given a good CLI interface). As long as your energy cost is okay-ish and you already have the hardware, that's quite a good use.