While there are Todo lists built into Gramps, this report was designed around the idea that you could attached a note to a person, family, place, etc. with the details of the task and mark/tag it Todo. That would also save time from having to duplicate information to identify the record you were working on.
While the existing Marker report (3.2) or Tag report (3.3) already does list any notes marked/tagged TODO, this new report allows you to sort by the referenced person, place, etc., or group them. Also the person's information is printed next to the note so you don't lose track of the subject.
This report also supports any custom tags you might have created.