Platforms > self-hosting Python apps

> For almost all of these options, autoscaling is a critical part of your hosting. While vertical scaling is important, scaling horizontally is an incredibly useful lever to pull. You need to be able to scale up to meet demand and scale down to keep costs under control.

Is there anyone on the entire Internet that writes about these things in terms that would make sense to programmers who have never done this stuff before? What is this horizontal/vertical metaphor, and why would non-entrepreneur hobbyists care?