Eloquent has a convenient feature called Accessors - you can define your own custom fields on top of existing in the database table. But then there's an Eloquent property $appends - should we use it or not? And what's the difference?
First - how Accessors work
For those who don't know or have forgotten: for example, if you have User model and fields first_name and last_name in the DB table, then you can create a function in app\User.php:
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So, in short - Accessor fields would work just by describing getAbcAttribute() methods, but if you want them to be returned in the list as well, then add them to $appends property.
More about Accessors (and related - Mutators) - in the official documentation.