As a developer, I like X because it's just another application. If the X server gets wedged (a very rare occurrence nowadays), everything else just keeps on ticking along. Simply kill the Xorg process and all is well.
Exactly so - the separation is clean and stability benefits. It’s a pain having to restart your X session but easier than doing a kernel reboot. MS with DirectX went the other way - to optimize performance (read games) the DirectX calls went right into kernel space so there is no separation.