This is sort of like how I learned by playing Civ that if you bum rush to Nuclear bombs and ICBMs you can simply bombs your enemies until they don’t exist anymore. Which is great fun in a game, but doesn’t exactly equate to IRL (but damn you Montezuma).
Anyways, here’s the deal; you would have the same amount of population no matter what. So whether my population was 1 person per square mile or 100 persons per square mile makes a huge impact. If you have a suburb of 100k people and a city of 100k people you can utilize less piping, less waste water, and less electricity more often since you often have dozens of families living in the same building which can utilize electricity more efficiently.
Not to mention that of course more people means needing more jobs, healthcare and education, but that’s also why you tend to have more of those things. It’s not like suburbs exist as self sustaining parts. They rely on cities with jobs to sustain them. Building higher density living spaces is a great way to solve many problems of modern American/Canadian life. I’m saying all of this as the opposite kind of person you’d find on this group since I live in suburbia and drive a giant truck. I just don’t want other people on the roads with me that suck ass at driving so I support public transportation to get them off the damn roads, plus it’s better for the environment.