There lots of functionality in the widgets. One thing I like to do is set up my own secret group where I can test the functionality of the widgets, particularly when responding to questions from users. While some of the functionality is easy to know and articulate to others, a refresher comes in handy other times.
You can also use responses to others to build documentation on how to use the widgets. You can highlight groups that are making good, creative use of some of the widgets.
On your question about watch a tag, if you set the place to your overall instance, it should search content across all of the spaces below that.