I recently flagged some questions for migration from StackOverflow to another StackExchange site (wordpress.stackexchange.com in this case). Some of these flags where declined by a moderator (reason: "Don't migrate crap") which was absolutely OK, as I wasn't aware of that rule then, and thought that these questions could be improved on the other site better than on StackOverflow.
However, for one of those flags the moderator stated: "[...] you should stop flagging WordPress questions unless you're actually active there [...]" Given that I was flagging some low-quality-questions for migration instead of flagging them as low-quality the moderator probably simply was annoyed by these flags. Sorry for that - now I know better.
I have quite some knowledge about WordPress and its ecosystem, having developed several plugins and themes myself. So I judge myself able to see whether a question is focused on Wordpress and its API or a general progamming question suited for StackOverflow.
So here's my question: Should I flag posts suited for other SE sites even if I am not active there but generally know the site's topic or not?