Yes, I’ve used it quite a lot.
Each topic-based section is slightly different, with different specific rules and a different community.
It is a good place to get very specific on-topic answers to specific questions, in the topics available. Particularly detailed answers to specific computer programming questions.
It’s especially good for finding specific answers by searching, through Google or its own search functions, for already-answered questions.
The downsides can include:
* It’s like the rules of Fluther’s General system multiplied by ten or more. You are expected to have researched your question and show that research, not be a duplicate, be on-topic according to their specific rules, be well-written and formatted. One of the rules about questions is that they need to be “appropriate for their Q&A format”, meaning that they reject almost all open-ended questions, requests for lists or opinions, or discussions (there is an ephemeral chat function which can be used for that, but it’s a secondary feature). Answers also tend to have rules such as requiring evidence or personal experience or other requirements or desires. If you fail to do those things, you may be downvoted, criticized, and your question or answer may be removed.
* The questions and answers and moderators all have point-reward/penalty systems, and some people take those, and their volunteer moderator positions very seriously, including enforcing the rules of each section (such as picky details about what is on-topic for the section or considered a proper answer).
* Speaking out about disagreement with the policies, especially if you mention it in a question or answer outside the Meta sections, may get you warned, censored, suspended or even banned.
* Directly contacting other members is not easy to do without breaking the rules or hoping someone is a user who hangs out in chat.