Using log file for SEO

I recently found out the use of log file in search engine optimization. Server traffic logs are files generated by the server in order to provide information about requests to the server for data. When a computer connects to a site, the computer, browser, and network will deliver some data to the site’s server itself to create a record that a file was requested. The file includes visitors information like keywords, the time user spends on your site etc. After reading this I quickly search through Google to find out the use of log file in SEO, and visited two three top search results. I found that there are many software which analyze the log file & create systematic results which is helpful for SEO. Now the first question arose in my mind is what is the use of Google analytics then. What is the difference between the two methods of collecting visitor's information? Which is the superior method? Going in the details I also read in some website that many SEO experts depend on the log file for the analysis of the site's performance and the usability of a site. Finally I came to conclusion that instead of depending on log file it is easy to use Google Analytics.