It really depends. There’s a lot of SPAs which are practically unusable on a bad connection simply because it’s a challenge to even get the whole thing loaded in the first place. There’s been several occasions where I’ve had poor cell connectivity and a huge chunk of the web was effectively off limits due to this.

So in addition to aggressive caching, I’d say keeping the app’s file size down is also pretty important to making it useful on poor connections. That’s frequently something that’s barely optimized at all, unfortunately.