> I think there's a lot of cases where you'll have a good amount of writes independent of audit lots. For example a chat system, or leaving comments on anything. There's a lot of scenarios where writes are common and this isn't a problem related to DB scaling. Each one of those writes will cause the user to wait a long time (location dependent) since your controller action will wait for your database to return before it sends an HTTP response back to the user. But I do agree there's tons of opportunities to take advantage of read-replicas for reads.

Yes definitely but many applications are 99.9% read, and stuff like chat doesn't really require instant <100ms responses. It really enables a load more performance for those usecases.

For many of those B2C sites $350/month would be nothing to save a load of latency and increase conversions. It's obviously not a solution for every single web app out there.