When it comes to loading time of your web application speed is always a major aspect. A simple web site that loads very fast is the best user experience. Speed is always in style. If you wonder whether your web site is fast or slow, you can always ask Google for that. Simply go to the Google PageSpeed Insights, enter your website URL and they will analyze it for you.
There are many articles, blogs, guides, books, poems and urban legends on how to keep your Rails controllers clean and simple. At job interviews that very question is being asked almost every time. Because of all that fuss around thin controllers even junior programmers without much of a practical Rails experience know THE answer.