The Watch Thread Command

  Watch Thread  (W)
Thread Pane icon
One handy off-line reading command is the Watch (W) command. 
When you watch a thread, Gravity goes through each article in the thread and puts its message-id and the message-id for all of its ancestors in the Watch List. The Watch Thread Rule will fetch all bodies in the thread and future articles in that thread.
·      The Watch Rule is a standard rule , which can be edited by advanced users.
For details see Ignore and Watch Threads Details

Here is a Trick:
You can use the Watch Thread command behavior to fetch all the non local article bodies in a thread, without permanently adding to the Watch List. Be aware this happens immediately if online, unlike tagging. It is simple (press W twice).

1.   Press W - the thread is added to the Watch List.

If ONLINE, Gravity starts downloading the article bodies.

If OFFLINE, Gravity tags the articles in the thread. You can purposely disconnect first if you want to tag rather than download.2.   Press W again, and the thread is removed from the Watch Thread list. If the articles are tagged. the tags will remain.