To be used when you know, or feel like, there are more tags to be added but don't know, or can't remember/find them.
More specifically, it should be kept until an image can be reasonably determined to be tagged to at least "Level 3" as per the howto:tag checklist.
Not to be used as an excuse for laziness; tag your uploads as best as you can.
Do also not use it when you find a badly tagged post. Instead, try to tag it as well as you can first. If you still think that tagme is needed afterwards, add it.
- annotation request
- artist request
- character request
- commentary request
- copyright request
- mecha to identify
- source request
- translation request
- instrument request
- topic #12251: "How do I tag this"