Most people I met who do double checks would simply return "not loggen in" and issue a WARN deep within the other 200 WARNs-per-second. That is IMHO a very bad

Most people I met who do double checks would simply return "not loggen in" and issue a WARN deep within the other 200 WARNs-per-second. That is IMHO a very bad usage of double checks. It gives a false sense of security and masks the deeper problem until it's too late. However, if you make the assertion fail loud, then it provides an additional security layer and should be used as often as makes sense.