Purpose of World Space Canvas width/height?

Just getting into setting up and using a Canvas, and I had a quick question. I’m using a World Space Canvas, because I want to create text that appears above certain in-game objects. And I noticed that when doing so, I have to option to set a width and height of the rect transform of my Canvas. My question is, what does this actually do? The text I add to the Canvas seems to display regardless of the width/height, even if I set it to 0. Are there certain values I should be using for this?

It defines the size of the object. TExt can be diplayed outside, but for example for Raycasting propuses define the object edges.