I've recently joined the SO community, and I use the flagging system very often. However, I have seen several questions related with game development, which I don't know if they fit better in GaveDev.SE, and therefore should be flagged as off-topic.
Usually, this posts require some specific knowledge of the framework at issue. According to this answer, if it is necessary more than general programming knowledge, they can be better served by GameDev. Nevertheless, there are almost 1.4k questions tagged with three.js on SO, while there are only 36 questions related with this library on GaveDev. I don't know if this is simply accepted, so start flagging them might be considered a misuse of this system.
As stated in its FAQ, GameDev.SE is the right place for game-specific programming issues (engine architecture, game-related APIs, networking, tools, etc). That was actually discused on Programming Questions: Here or "Belongs on Stackoverflow"?. I do understand the point of this, as well as it is possible some overlap among SE sites. For example, I've recently answered a question about collision detection, which I consider a borderline. But I think answering questions about animations, textures, etc. is a step further.