ALT + ENTER is usually used to enter a line-feed in a cell when in edit mode.
BUT.......it does quirky things when used not in Edit mode.
It will repeat the last action taken in most cases.
Close a used workbook......open it again......hit ALT + ENTER and the workbook
will close.
Open a blank workbook then hit ALT + ENTER to keep opening new blank books.
Put a border around a cell. Move to a blank cell and hit ALT + ENTER to get a
border around that blank cell.
Some would call it a bug, others and undocumented feature.
I use it only when editing a cell so's I don't get unexpected things
happening.
Gord Dibben Excel MVP