I think of it as indicating the function name and parameter list are a unit (it's foo(object), not foo (object)). I've always liked that style.

When I see people write

    'some %s %s text ' %('x', 'y')

my first thought is "% is not not a function".

I'm reminded also of (and agree with) the Crockford convention in JavaScript recommending a space in

    function () {...}

but not in

    function foo(object) {...}

But conventions are are a choice made; most times it's easier to adopt them and move on.