Advantages

It keeps the session in the database and not on the Web Server (IIS) making the server memory free for other usage.

It allows the session objects to be shared among other applications like ASP, PHP, etc.

Leads to Web farming and web gardening.

Disadvantages

Brings the performance Issues into the picture due to the Database round trips.

It also goes through the process of Serialization and De-Serialization every time, which is another overhead.

It forces all the classes whose objects are going to be stored in session declared as Serializable().

It forces you to define the class in a specific way.

It cannot use any other database except the SQL Server.