I couldn't agree more, it helps you write clean code, and catch misspellings in variables (especially case-sensitivity issues with variables).
$firstName = $theUser->firstName();
This would generate a warning, because $firstname is undefined (should be $firstName).
Another frustrating thing is when evaluating open-source code which was NOT developed with error_reporting E_ALL, and there are hundreds of errors all over the place, and then I need to make a custom .htaccess file to disable errors for a certain dir, and generally have a bad impression of the software before I even try it out! So, it's definitely possible to write functioning code without error_reporting on strict mode, but keep in mind that other people who use your code might see this as sloppy.