Memories or Sources?
Tagging Memories identifies people in photos and documents and links them to their Family Tree profiles.
Tagging Sources put the important sources for a piece of information right on that piece of data so you do not need to dig through the entire source page to find it. For example in the new profile pages, you can tag a census record right to a census event like this:
The tagging is what puts the sources in this box. You can even click on the source name and open it right here and read all the information in the source.
Unfortunately I see too many people tag every since source to every bit of date. It loses all its usefulness if all 50 source on a person are tagged to the person's name no matter what the source is. A small handful of the most important sources would be sufficient.
In my opinion, almost no one understands the true purpose of source tagging. Theoretically, the tag is intended to identify the specific event that the source record is evidence of proof for that event. Unfortunately, the familyseach software default is usually yo fill in all the tag boxes which contributes to tagging being less than useful. (an example is Census records - the birth tag gets filled in even though the source record is not proof of a birth date, but merely the age of the person at the time of the census)
please clarify the context of your question.
"tagging" can me a lot of different things to different people and different contexts