The PHP E_WARNING constant represents run-time warnings that alert developers to non-fatal errors without halting script execution. These warnings typically arise from minor mistakes, such as referencing non-existent files, incorrect or missing function arguments, or improperly ordering HTTP headers and body outputs. Addressing these warnings is considered a best practice, as they can lead to more significant issues over time. During development, enabling E_WARNING through the error_reporting() function helps identify potential bugs, and using error_reporting(E_ALL) is recommended to display all errors. An example of an E_WARNING is provided, where a var_dump() function call lacks a required parameter, showing how such issues can be fixed by inspecting warning messages and adjusting the code accordingly. Tools like Rollbar enhance error management by automating error monitoring and triaging, thereby facilitating smoother deployment processes.