The main advantages of log file analysis is that the data is already logged by your web server and not sent to a third party. Every transaction is recorded by the web server regardless of the visitors browser except where the cache is used. Also this data is directly on your server in a standard format so you don’t rely on a third party server to collect anything. Another advantage is that log files provide information about visits from search engines spiders and bots as well as failed requests which is very important if you want to optimize your website and fix thing like broken links or other errors that occur. Have a look at an example of the reports produced by Awstats and Webalizer.