On the other hand, self-hosting everything doesn't let you take advantage of caching.

What I mean is, if two sites use the same resource, and if both sites fetch the resource from the same URL, the resource will likely be cached by the browser once and reused again and again. This can be huge for load times when users visit a website for the very first time.

Or at least, this was the argument that was floating around in the community, when I used to do web dev. It's been a few years since, and I'd be interested to see if people have other arguments for/against this.