What dose Model::unguard() do in the database seeder file from Laravel 5?

I am trying to find out what is the purpose of Model::unguard(); and Model::reguard(); in the DatabaseSeeder.php file that ships with Laravel. I have gone through the seeding documentation at laravel's site and googled but in vain.

So what is the purpose of Model::unguard();? Assuming Model::reguard(); is just the opposite.

via Chebli Mohamed