This page shows ways to configure drag down behavior:
Drag down in all directions
Notice the little square (fill handle) in the corner of the selected cell. You can drag it (drag-down) to repeat the values from the cell. Double click the fill handle in cell B4 (value "30") to fill the selection down to the last value in neighbouring column, just like it would in LibreOffice or Google Docs.
Drag down in vertical direction only without creating new rows
In this configuration fill handle is restricted to move only vertically. Additionally when it comes to the edge of the table bottom it preserves creating new rows.