There are numerous advantages to server scripting languages over client side languages in regards to creating web sites that are more compelling compared to a standard static site. Server side scripting are scripts that are executed on a web server during the compilation of data to return to a client. These scripts allow developers to modify the content that is being sent to the user prior to the return of the data to the user as well as store information about the user. In addition, server side scripts allow for a controllable environment in which they can be executed. This cannot be said for client side languages because the developer cannot control the users’ environment compared to a web server. Some users may turn off client scripts, some may be only allow limited access on the system and others may be able to gain full control of the environment. 
I have been developing web applications for over 9 years, and I have used server side languages for most of the applications I have built.  Here is a list of common things I have developed with server side scripts.

List of Common Generic Functionality

• Send Email
• FTP Files
• Security/ Access Control
• Encryption
• URL rewriting
• Data Access
• Data Creation
• I/O Access

The one important feature server side languages will help me with on my website is Data Access because my component will be backed with a SQL server database.

I believe that form validation is one instance where I might see server-side scripts and JavaScript used interchangeably because it does not matter how or where the data is validated as long as the data that gets inserted is valid. However, I would have to say that my personal experience would have to sway me in deciding what type of languages to use for form validation because they both have advantages and disadvantages based on the each situation.