Mostly while working with Magento, you end up with serious errors or broken stuffs. So, Magento Error Logs come to the rescue here. Whenever you have a serious error on your site, you can just view your error logs and debug the error and get rid of that situation. As simple as it is.
Many of you may be wondering, how to switch on Magento Error Logs or view it. So,here are the simple steps :

1) Turn on your logging: Admin
> Configuration > Developer > Log Settings > Enabled = Yes

2) Watch your var/log/system.log and var/log/exception.log for raw information from this.

You may run into file permission errors, so you might need to set your folder permissions appropriately.