I am surprised the reasons for planes being to fit in odd bit sizes. Although I suppose that is a reason.
Planes are a nice abstraction, because they allow you to use the concept of a raster surface for all kinds of things. These things might be bits of colour, but they might be metadata in an image analysis program, or a masks in a graphics editing program, z-buffers for 3-d graphics, or really anything.
(Admittedly, I am talking about an abstract concept of "plane", whereas the original article is presumably talking about the concrete behaviour of hardware.)
Planes are a nice abstraction, because they allow you to use the concept of a raster surface for all kinds of things. These things might be bits of colour, but they might be metadata in an image analysis program, or a masks in a graphics editing program, z-buffers for 3-d graphics, or really anything.
(Admittedly, I am talking about an abstract concept of "plane", whereas the original article is presumably talking about the concrete behaviour of hardware.)