Set `positionFormat` for reduced memory use?

https://deck.gl/docs/api-reference/core/layer#positionformat

> `positionFormat` ("XYZ"|"XY", optional)
>
> The format of positions. This prop is currently only effective in PathLayer, SolidPolygonLayer and PolygonLayer.
>
> Default 'XYZ'.

Does deck uses an `XYZ` position format by default? And, if so, does that mean it allocates an empty Z buffer for all coordinates? If so, we should pass `positionFormat: XY` whenever we know we have 2D data (which we always know). Do we get a 33% memory reduction?

Perhaps we should set this in deck.gl-layers instead of here.

cc @felixpalmer for thoughts