I had the same question.
I didn't see any information about differences between [bd] Tag Me and native Xenforo tagging in the Resource description
here.
I take it that all the features listed are features not available in native Xenforo 1.2 installs.
How about something like this to help newbies like me:
[FEATURES]
As of Xenforo 1.2, Tagging users is a part of Xenforo's native code.
[bd] Tag Me adds the following features to Xenforo 1.2's tagging:
1. Tag other user easily with @ syntax in profile posts, profile post comments.
2. Tag many users at once with @user_group syntax!
3. Tagged user will receive an alert and email if enabled
4. TinyMCE Quattro support.