SQL Server or SQL Express errorlog files can reveal what is the health of your site
I/NET site with Full SQL or SQL Express installed for the database.
Ensuring processes within SQL are completed successfully.
Errorlog file is so large it is filling the Hard Drive.
View the SQL Server error log to ensure that processes have completed successfully (for example, backup and restore operations, batch commands, or other scripts and processes). This can be helpful to detect any current or potential problem areas, including automatic recovery messages (particularly if an instance of SQL Server has been stopped and restarted), kernel messages, or other server-level error messages.
View the SQL Server error log by using SQL Server Management Studio or any text editor. For more information about how to view the error log, see How to: Open Log File Viewer. By default, the error log is located at Program Files\Microsoft SQL Server\MSSQL.n\MSSQL\LOG\ERRORLOG and ERRORLOG.n files.
A new error log is created each time an instance of SQL Server is started, although the sp_cycle_errorlog system stored procedure can be used to cycle the error log files without having to restart the instance of SQL Server. Typically, SQL Server retains backups of the previous six logs and gives the most recent log backup the extension .1, the second most recent the extension .2, and so on. The current error log has no extension.