Why should you update APP_URL from from http://localhost?
Your site will work fine without updating it - until you start using jobs and commands. When viewed in the browser (such as http://example.com, http://localhost:8000) Laravel can work out what your actual URL is. However, when you start sending emails, running commands and more it won't know what is your actual URL and will revert back to whatever is set in APP_URL (
config('app.url')). So make sure you keep it correct, even if it seems to work ok with localhost.