Emacs Elements has a short video on sparse trees. The TL;DR is that sparse trees give you a method of filtering an Org file to show only the information that you’re interested in. The information can be random text, a tag, a property, deadlines, dates, or date ranges.
Unfortunately, the video doesn’t capture the full power of sparse trees. It makes it seem as if all it does is highlight the matches in the visible buffer but sparse trees are actually much more powerful. If you have a large file, it will hide any non-relevant data except for context. The rules for what constitutes “context” are slightly complex so you should take a look at the documentation for the full story.
My only complaint is that I can’t find a way to restore the original buffer after invoking a sparse tree filtering other than reloading or rebuilding the file. You can turn off the highlighting but I can’t figure out how to get the original buffer back. This is Emacs so I’m sure there’s a way but I haven’t found it1.
Another nice feature of sparse trees is that you can “stack them”. That is, after forming a sparse tree representation of the buffer you can refine that representation with further filtering.
The video is only 5 minutes, 12 seconds so it’s easy to find time for it. It will give you a good overview but you really need to check the documentation for the complete story.
UPDATE :
I just noticed that the fix for restoring the previous buffer state no longer works so we’re back to no solution to this problem.