Quite frankly - and I don't mean to offend - but I find discussions like this incredibly stupid.
Everything boils down to how good the story you're telling is. A writer won't inspire an artist by adding or subtracting description until it's just right - like he's making a porridge. A writer needs to spark the artist's imagination. Start thinking or worrying about rules and your writing becomes very clinical.
God no, being clinical doesn't help at all.
You eventually reach a point when you've been writing long enough that things become instinctual, when you just naturally know what is too much or too little.
But even when you've been very detailed, an artist can come up with an idea which works a hell of a lot better. I've been in situations where an artist has suggested moving a panel over to the next page or dividing one panel up into five and it's worked beautifully.
So, even when you are being exact in a script, it doesn't mean you can't be open to change.
A writer and an artist should be collaborators, equals when it comes to creating, and so being open to discussing changes is always a good thing.