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.

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.