The unattended installation feature allows for unattended installs using a batch (.bat) file and an associated initialization (.iss) file. By placing the SQL Server compact disc in the computer or pointing to a network share and running the batch file, SQL Server will be installed with the options specified in the initialization file. Microsoft includes sample .bat and .iss files on the SQL Server compact disc for a typical, custom, and client tools only install. These can be edited with a text editor to specify options specific to your environment. An option is also available on the Advanced Installation Options screen during the install that specifies Record Unattended .ISS File. When this option is selected, the options you specify during the "install" process are saved to a setup.iss file and SQL Server is not actually installed.
The idea behind an unattended install is not that you can go for coffee instead of answering the prompts during an install, but rather that you can repeat an installation with the same options for multiple servers. If your reaction to this is anything like mine was, you are probably ready to move on to the next section because you assume you will never use this. Most sites just don't have that many servers. However, consider the advantages of having a repeatable install for even a single server. If the server ever needs to be installed, if you have saved the original unattended installation files, you can run them and be assured that all the options will be the same as for the initial install. This is especially important for the code page and sort order selections. It also will be one less thing to worry about during an already stressful system recovery. In addition, unattended install is useful for application vendors who require a certain configuration for the application to function properly. By providing the client with a set of unattended installation files to run, he is assured that the SQL Server setup is done correctly. The unattended install also ensures you can reproduce a "correct" install in the test environment when you move into production.
If there is a chance you might have to repeat an installation, I recommend using the Record Unattended .ISS file option to generate scripts to automate your install, and then running the batch file to perform the actual install. If you already have a server installed and would like the installation configuration file, the setup.iss file in the MSSQL\install folder contains the original setup options. Unattended installation ”it's a good thing.