The purpose is to make use of a dimension of the visual space previously unused to make diagrams more expressive.

Even if it's something simple like a node turning from green to red to convey it's shutting down. Maybe something like that before animations would be a text saying, "this node will shut down now", which takes reading/zooming into text.

I also think it can, if used well, result in diagrams that ⋆⋆spark joy⋆⋆. People like to see diagrams like that, even if it's not more utilitarian. I think sketch mode is an example of this. It changes the font to an objectively less readable one, yet I often hear people make all their D2 diagrams in sketch mode.