I recently asked this question which got closed because its answer was based on opinions. But that was exactly the point of my question, and hence the usage of tag of "convention". So I am not sure why it got closed.
Speaking in general, the existence/non-existence of a tag does not imply that a certain question is on-topic/off-topic, respectively. This is instead decided by the Phys.SE community, e.g. via vote-to-close/vote-to-reopen, or e.g. via Phys.Meta policy posts.