I think it caused more problems than it was worth. It generated a lot of "why doesn't my program work?" questions.
It's one of those things not all systems support.
UNIFIED
public static final StageStyle UNIFIED
Defines a Stage style with platform decorations and eliminates the border between client area and decorations. The client area background is unified with the decorations. This is a conditional feature. If the feature is not supported by the platform, this style downgrades to StageStyle.DECORATED
` NOTE: To see the effect the Scene covering the Stage should have Color.TRANSPARENT
Since:
JavaFX 8.0
It was removed as it didn't work properly with Windows 10. It caused the forms to look empty. Setting the style to UNIFIED is now equivalent to setting the style to DECORATED.