Although this may sound strange at first, some large sites have to deal with multiple thousands of logs per second and are experiencing difficulties keeping them intact for a long time or detecting errors within them.
If the option “dontlog-normal” is set on the frontend, all normal connections will not be logged. In this regard, a normal connection is defined as one without any error, timeout, retry nor redispatch. In HTTP, the status code is checked too, and a response with a status 5xx is not considered normal and will be logged
Of course, doing is is really discouraged as it will remove most of the useful information from the logs. Do this only if you have no other alternative.