Server log file means it is a common record book is a listing of everything that goes in and out of a server. You know it as a ledger of several requests made by crawlers and real users of a web page or website. We will see accurately what links Google is crawling on your site. This log analysis will reduce the wastage and supply relative content to users.

Google webmaster blog says:
"Wasting server resources on pages like these will drain crawl activity from pages that do actually have value, which may cause a significant delay in discovering great content on a site.