Guards are meant to define how Laravel should store and retrieve information regarding (authenticated) users.
e.g. web, api are standard guards shipped with Laravel. You could create your own nova guard if you use Laravel Nova etc.
You'll probably need Policies in your case, see https://laravel.com/docs/6.x/authorization#creating-policies.
A user will have an ability to do something, let's say update a Photo. But to be able to do so, the user should belong to the same organisation as the Location.
In other words:
public function update(User $user, Photo $photo)
{
return $user->organisation_id === $photo->location->organisation_id;
}