Option to "Freeze" parts of the page when scrolling: a bit like Excel Freeze Window to keep a few top rows and/or a few left columns in view when working on a remote part of the page.
Helpful for diagrams which have clear "axes" e.g. time (as an X axis or as a Y axis on sequence diagrams), Swimlane titles, Function names on sequence diagrams, etc.
Workaround is to make a copy of the relevant axes markers, paste it, group it, and then drag it where needed, but you have to remember to remove it before "publishing" (you can stick your moveable axes into a non-printing layer which helps a bit).