> if you follow (the Rails Guides) start to finish, you'll have a Rails app in production. And it isn't just hello world. Your app will have authentication, caching, rich text, continuous integration, and a database. That's a real application.
These features are great for established apps like GitHub and Airbnb, but if you're making a tiny startup, and want to test ideas quickly, I wouldn't spend time on CI, caching, Rails's authentication (use extremely feature rich Devise gem), Rails's 'turbo' features, and writing tests. These are all good things for medium or larger apps, or well-funded apps with a long run way, but are usually cost-benefit negative for small apps.
Turbo saves a fraction of a second on many page loads, but can add days of development time for those not fluent in javascript when it causes some core functionality to not work (e.g. devise's Log out!). Testing is very important on large apps but for quickly flicking a few ideas together and getting it in front of users; unless you're a banking or healthcare app, they can probably be postponed until you have traction.
Be mindful of your size and timelines and don't succumb to 'default bias' where you use things simply because they were there out of the box. Feel confident to say 'no, we don't need that (for now)'.