Advantage of the "app":
Rather than to go more step by the administration menus, you can finish WhatsApp directly.
Unfortunately, you can not quit WhatsApp directly (unless you have his phone rooted - but because invalidates the warranty). But so it works out pretty easily. Have Fun.
Thanks again to Sven for support.
Oh, because of the message that errors can occur: So far I have not found any WhatsApp error - otherwise please message.