It is advised to disable unused modules in Magento for website optimization. Also while troubleshooting issues we can temporarily disable module(s) to see which module(s) is/are causing the issues.

Let see how we can disable the modules in Magento:

1. Login to Magento admin and go to Admin >> System >> Configuration. On the left hand side click on the Advanced section under Advanced tab.

All of our custom developed modules are stored in the app/code/local folder. If in case an error has not been logged in error log files and to troubleshoot we want to check whether one of our custom modules is causing problems or not, so in that case we should first disable all local modules and see if the site is working or not.