【http://gokanx.wordpress.com/2013/06/15/how-does-web-analytics-works-under-sharepoint-2010/】
You need to plan before you configure Web Analytics Service Application for SharePoint.
Why? The reason is simple, and Joel Oleson explains the reasons on this blog:http://www.sharepointjoel.com/Lists/Posts/Post.aspx?ID=515 
The issues have not improved on SharePoint 2013. Check this out:http://www.sharepointjoel.com/Lists/Posts/Post.aspx?ID=655
My client obviously wanted to have Web Analytics to get information about their web pages when I was on vacation. So they configured the Web Analytics with a SharePoint Developer.
But they couldn’t open it because it was greyed out. So they thought everything went wrong and SharePoint isn’t working, and they can’t get data …
Web Analytics on SharePoint 2010
But actually as many of yours know for getting you have to start first of all the 2 services “manually”
- Web Analytics Data Processing Service
- Web Analytics Web Service
Web Analytics on SharePoint 2010 2
Secondly you can get data/reports by:
- Central Administration
- Site Collection Settings
Web Analytics on SharePoint 2010 3
These are the steps that occur:
Web Analytics on SharePoint 2010 4
- User request a page and action gets picked up by the Web Analytics service that runs on SharePoint
- The Web Analytics service logs this in the “.usage” files
- A Timer job called “Microsoft SharePoint Foundation Usage Data Import” that by default runs every 30 minutes imports the logs into the staging database.
- Each night the “Microsoft SharePoint Foundation Usage Data Processing” Timer job runs and transforms the data into the reporting database
- The last run time of the import from staging and the aggregation is logged in the Settings table in the Reporting database