This is a reposting of what I wrote on the Acquia Dev Center blog in 2016, Should I disable PHP warnings and notices?.

Many developers who work on Drupal (or other web/PHP) projects have error reporting disabled in their local or shared dev environments, for a variety of reasons—some don't know how to enable it, some are annoyed by the frequency of notices, warnings, and errors, and some don't like to be reminded of how many errors are logged!

There are a few important reasons you should make sure to show all errors when developing, though: