WoW - why improve Inscription after 600?

What advantages of Inscription at 700 comparing to Inscription at 600?

According to wowhead there are no recipe, which needs Inscription above 600.

I heard that war paints became cheaper, but I would like to know exact dependence "costs vs Inscription level".
And aren't there any other advantages?

P.S. I heard that the yield for war paint increases from 4 paints per 10 pigments up to 10 per pigments, when inscription level increases up to 700. If one suppose linear dependence, and that at lvl600 you get 4 paints, that at lvl617 you must have 5, 633->6, 650->7,667->8,684->9,700->10. But this is not the case, my hero at 640 level and can create only 4 paints from 10 pigments. P.S2. I have lvl700 inscription now, but my ability to create paints is limited to 4.

Since Warlords of Draenor all new profession recipes are usable with a skill of one in the profession. The only difference is in the daily cooldowns for the professions.

For Inscription this is War Paints:

Additional paints are created when your Inscription skill is 600 or higher.

Up to skill level 600 you generate 4 War Paints per use, until level 700 this increases to 10 War Paints per use. This scales more or less linearly, you get 5 with skill 600 and one more with every 20 additional skill points with some random variation.

The only advantage I can see outside of the increased War Paints is to meet the criteria of the Grand Master of All achievement (raise each primary profession to 700).

First, I just levelled up my inscription to 700.

Then, in "Inscription window" I still see that I can create 4 paints using 10 pigments.
But as a matter of fact, when I run transformation I get 10 paints.

Also, I contacted support, and been explained that even at lvl700 you are not guaranteed to get 10 paints for 10 pigments. But when you run transformation you have a chance get additional paints over mentioned 4.

So I conclude, that with leveling up inscription you:
1. Get new achievements, like Ben told.
2. Increase your chance to create more that 4 war paints per cast.