There are lots of ways it can be used - it all depends on what you use DT3 for
In one of my databases, I use annotations to create bookmarks to locations in a large document that I frequently refer to
In another database, I use annotations to mark key parts of a large document before I sit down to write a consulting report with my opinions on the document
In another database, I use annotations to give editing advice to my staff as they progress through writing/creating a new document
There are of course so many other possibilities depending on the circumstance. Remember that you can insert a “Backlink” in the annotation file which sends you back to a specific page in a specific document - that is a key feature for me
And of course you can edit the color/font/etc of the annotation text just as with any Rich Text content