I think it helps to promote services (in this case a P2P service which I think deserves a bit of publicity) to people who don't speak or understand English very well. It's not just the active users of the forum, but also those who come to the topic from a search engine who will benefit from the translations.

Personally, I always keep an eye on my topics, and if anyone has any questions to ask in French about any of the topics I've translated, I'll be happy to answer them, because if I don't believe in the said project, I won't translate their ANN. If I don't have the answer, I can tell them who to contact, and do it for them if necessary.

I don't think local boards should be underestimated, even the least active ones can hold useful information for those who arrive there via a search made in their mother tongue, even without being active on the forum itself.