I think it is a useless tag, since the majority of questions are already about psychology, and we have more informative [subtype of]-psychology tags already in place.
I also fear that having such vague tags encourages bad posting, since people don't take the time to figure out which tags are best to use; i.e. where their question actually fits. However, it seems that when a 'psychology' tag is unavailable, people just tag things they don't know how to tag as 'cognitive-psychology', making it our general dump tag. So maybe we should consider creating a 'general-psychology' tag? Maybe it will clean up the 'cognitive-psychology' tag, or maybe it will increase the rate of poorly tagged questions.
So the two questions for the community:
Should we eliminate (by re-tagging) and ban the 'psychology' tag?
Should we have a 'general-psychology' tag for people that don't know how to tag their psych questions?