Tracking your site’s PHP errors is an excellent way to manage and troubleshoot unexpected issues related to plugins and themes. While there is no definitive method for handling errors, there are some "best practices" that should be implemented in all PHP applications.
An "error" is an expected or unexpected event that occurs when your PHP code is running. An "expected" error can be a database query that returns no result or an html form that is missing values for designated required fields. An "unexpected" error is one that assumes a particular application state which, for some as yet unknown reason, does not exist. The most obvious unexpected error is a database that is not running or a missing file that one of your scripts expects to find.