The advantages of using session state are as follows:
It is easy to implement.
It ensures data durability, since session state retains data even if ASP.NET work process restarts as data in Session State is stored in other process space.
It works in the multi-process configuration, thus ensures platform scalability.

The disadvantages of using session state are:
Since data in session state is stored in server memory, it is not advisable to use session state when working with large sum of data. Session state variable stays in memory until you destroy it, so too many variables in the memory effect performance.