The command provides much of the information produced by phpinfo(), including the PHP build, extensions, settings and configuration-file locations. It can reveal which php.ini file the current command-line runtime reads and whether a setting has the value you expect.
Like php -v, it reports the binary that your shell selected. A PHP-FPM pool or web-hosting handler can load a different configuration or even a different PHP release. That means php -i cannot confirm the live website configuration on its own.
The output can include internal file paths, environment details and settings that should not be shared casually. It is useful for local troubleshooting, but copying the full output into a public ticket can disclose unnecessary information.
Compare the CLI results with the actual web handler when diagnosing a site. Save only the relevant lines, remove secrets and check which configuration files each runtime loads before changing any settings.