Named arguments allow passing arguments to a function based on the parameter name, rather than the parameter position. This makes the meaning of the argument self-documenting, makes the arguments order-independent, and allows skipping default values arbitrarily.
Another RFC proposed for PHP 8. Not sure exactly how I feel about this one yet. I like the idea but Jeremy also pointed out that then params become part of the public API. Need to think about this one some more. -Chrispian