Actual difference between "tracked" and "watching first post"

[nordize]

It says what tracking means right there

A count of new posts will appear next to the topic.

But (like I said in my post) both “watch first post” and “tracking” show a count new posts next to the topic (tested in 1.8.0.beta10+57) … so I’m not sure what’s the difference between the two, it seems “watch 1st post” subsumes “tracking”.