The Compilation feature of Magento will allow you to compile all files of a Magento installation in order to create a single include path to increase performance.
The performance increase is between
25%-50% on page loads. In order to use this tool, the directory
includes and the file
includes/config.php must both be writable.
You can temporary disable it in Go admin side »
System » Tools » Compilation by clicking the Disable button and the Compiler include path will be disabled. Then, after the extension installation run the compilation process again.
Please, make sure that you use the
Run Compilation Process function after the installation, not the
Enable Compilation - otherwise, you are likely to get backend fatal errors.
Before you make any changes to your Magento installation you should always disable compilation.
Once the changes are made, run the compilation process, and then enable it.