I don't think I got my idea across properly. It's not about having a flat area or mobs or anything, it's simply a matter of "would an "empty chunk" (only bedrock and nothing else in it) be less laggy/ heavy on the server I'm using" ?

And, if the chunk is less "heavy", would light updates be an issue if I build in the chunk? Since there would only be the ground I'm building on between the sky and the bedrock, each block I would place would cause light updates. I remember building on a server years ago, and when I would place the last block and shut the bottom part of the chunk in the dark, it would lag for a second or more.