Making a huge selection with mouse in LibreOffice spreadsheets even today goes faster if you move the mouse while dragging one endpoint of the selection over the spreadsheet borders which causes the sheet to scroll. Likely the very same cause: there's a timer or other repeating tick to scroll content at a reasonable speed but the sheet is also scrolled when input events wake up the same loop.
I remember this with any selection in windows on at least 3.1/95/98/SE.
This happened if you kept the mouse just inside the window and moved it about 10-20px up and down in/out pf the window in the direction of the selection.
It was a way for me to scroll faster than with the wheel or cursors on web pages if you selected some text and then kept the selection on the end of the screen and moved the mouse wildly in the edge of the screen.
As I was younger then, there was probably a better solution to do this but I was not aware of it.
