#2471 implemented Range{From,Full,To} but RangeFull was omitted for lack of use cases.
Here is a use case:

I have a grid API where a user can add rectangular items with range syntax.

let mut grid = Grid::new();
grid.push(2, 3, item1);
grid.push(.., 2, item2);
grid.push(1, ..=1, item3);

This represents

    2
3 3 2
    2   1

The full range .. is very handy notation for filling up the space.
RangeToInclusive ..= can always be replaced by RangeTo, but it's naturally expected for ergonomic API that any place accepting RangeTo also accepts RangeToInclusive.