why use a relationship manager?

<?php

namespace App\Filament\Resources\InvoiceResource\Pages;

use App\Filament\Resources\InvoiceResource;
use App\Models\Invoice;
use Filament\Forms\Components\Group;
use Filament\Forms\Components\Section;
use Filament\Forms\Components\Select;
use Filament\Resources\Pages\Page;

class ViewInvoice extends Page
{
    protected static string $resource = InvoiceResource::class;

    protected static string $view = 'filament.resources.invoice-resource.pages.view-invoice';

    public ?Invoice $record = NULL;

    public function getTitle(): string
    {
        return __('invoice-resource.viewInvoice.title');
    }

    protected function getFormSchema(): array
    {
        $tab = array();
//        if ($this->record->method_payment == Invoice::BANK_TRANSFER) {
        $tab = [
            Group::make()
                ->schema([
                    Section::make(__('invoice-resource.section.invoice_information'))
                        ->relationship('quote', 'this')
                        ->schema([
                            Select::make('name')
                                ->options(function () {
                                    dd($this->record->quote);
                                    return $record->quote;
                                })
                                ->label(__('artist-resource.field.name')),
                        ])
                ])
        ];
//        }
        return $tab;
    }
}