Code rots over time. While you're busy adding new features to your app, you might be forgetting to throw out the old. This is a friendly reminder to sweep out the garage and get rid of the things you don't need.
You don't have to scour through every line of code to get results. Here are some areas you may be able to score a quick win.
Move any third-party assets in `app/assets` to `vendor/assets`. Putting third-party assets in your `app/assets` directory is generally a mistake, and that's ok. Clean up and put them where they belong and you'll be fine.
Remove any CSS files and/or rules no longer being used. The level of detail you achieve here depends on how much time you want to spend. Removing unused CSS may be as simple as removing some files you're no longer using. If you want to dive into removing rules, there's a great tool for that called deadweight.
Get rid of legacy models/database tables. A few legacy models may have leaked into your code base early on in the life of your app (when you're under rapid development). That's ok. Figure out what they are and get rid of them. Write a migration to remove the table, too.
Find any unused partials. If you're refactoring quite a bit, you might forget to remove some unused partials. Check out this gem to remove unused partials.