I don’t have personal experience in this, so obviously I can’t speak with any authority. But I have heard from colleagues that tons of little factors can dramatically affect user engagement. For example, even a couple dozen milliseconds of longer load times can push a noticeable number of users away from your app.

Undoubtedly some people will be put off, but think of how often Reddit used to go down -- still got pretty big. And Twitter already has all the newsmakers people want to see. If your goal isn't necessarily user growth it makes sense

But how much money are you willing to spend to get that 1% that will be turned off by a fail whale or latency?

I have personal experience with this. The metrics (as much as I despise using them as a source of truth) undoubtedly show a very strong positive correlation between better load times and user retention.

This is true, an insightful add-on point, and one Larry Page’s favorite pearls of wisdom.

Very few people are going to be converted to paying users if they start to see downtime or breakages. No one buys into a failing app.

true. if twitter, Facebook, reddit, and hackernews go down for a couple days it wouldn't affect me at all. if GitHub and npm went down I'd me mildly annoyed but could still work.

As long as you don’t mention Stack Overflow, I agree!