Say something has 2 potential topics, in the practical case to which I am applying the answer to this thread: I want to ask a question about Wordpress & SEO. The question is directly about how 1 feature in WP impacts SEO. In fact, it is the tags feature of WP, so it also has to do with Keywords. Does it go in SEO, Keywords or Wordpress? Either? Thanks a lot.
General SEO questions go in SEO. If it's very specifically related to Wordpress, it would probably be best in the Wordpress area. But it depends on how you ask the question. If the question is specifically about a WP feature, wordpress. If the question is about SEO more generally and the site just happens to be affected by a WP feature, then SEO. There's no hard line. It's one of those things judged on a case by case basis.
I would ask in the more active forum since it increases your chances of getting a reply. In this case the SEO forum is the more active and appropriate one.
Posting in the more active forum when it is not the best fit often will result in "Thread started in wong category" infraction.