Using ::class in Model's $returnType instead of string - bad?

Before I go abound and create a PR for a documentation change, I have to ask if I have misunderstood something.
I am refactoring my CI 4.1.9 project in PHPstorm and found out that

PHP Code:

protected $returnType = App\Entities\SomeEntity::class; 


 is an excellent way of writing this instead of specifying this as a string 

PHP Code:

protected $returnType = 'App\Entities\SomeEntity'; 


As I read it from the documentation, "::class" expands at compile time so it can't be for performance reasons - https://www.php.net/manual/en/language.oop5.basic.php
What am I missing?
/Mattias