If the site you have is an interactive site, then you will probably need persistence. This is especially true for sites that require some type of login. If the site you are running is static, serving only static text and images, then you may not need persistence. In most cases, persistence cannot hurt even if you do not need it.

The session handling mechanism for many website programming languages (ASP, PHP, and so on) are known as “stateful”. There is a unique session established for the user, and that “state” is kept on the same server. This stateful information, which can include everything from login credentials to the content of a shopping cart, is typically not shared among servers. So, when using multiple servers it is important to keep an individual user tied to a specific web server for the duration of the interaction, and that is where persistence comes in.