How justified is the use of foreign key in Laravel?

Question

Database

Hello.
We are talking about this construction (in migration):

$table->foreign('user_id')->references('id')->on('users');

that is, in theory, it will work without it, if you add to the model

public function user()
    {
        return $this->belongsTo('App\User');
    }

Yes?
How much is a foreign key really needed?
I have just started learning Laravel - I'm looking for the simplest solutions without unnecessary entities.
Thank you.

Answer 1

Will. But sudb will not know that this is a foreign key, so the goodies like "when we delete a section, elements are deleted" will not work. And this is often necessary