This setting enables the logging of occurrences that have occurred in policies governed by the proxy option profile that this setting is enabled in. As stated elsewhere in this document there can be a number of reasons that a web site may have a certificate that registers as being invalid. Because some administrators decide to allow users to access these sites it makes sense to keep track of when it happens. This does not prevent the accessing of web sites with an invalid certificate. It just allows for logging when it happens.