That doesn't let you tell graphviz how large you want to draw each node, right? Just how large graphviz would draw them? What I'd like is a way to take styling and drawing outside GraphViz. It's important (for what I'd like) that graphviz know how large each node is going to be so it can route around them. If you apply, say, a typeface or padding even very slightly different than what graphviz was using, or if there are just slight differences in, say, how a given browser renders a <div>, it could change the size of the rendered nodes, and you end up with edges drawn under/over nodes.
Much cleaner (and way more useful) to be able to tell graphviz "this is how large I need this node to be, and that one this size, and the other one such-and-such, and they are connected thusly, now please give me coords for a layout"
This isn't just for looks, either: if you want the resulting graph to be interactive, and perhaps even graphically (drag-n-drop) editable after the initial graphviz auto-arranging, you're probably wanting output that's not exactly in graphviz's wheelhouse. You want to tell it node sizes and have it tell you where to put them.
https://graphviz.org/doc/info/output.html#d:plain