Advantages and Disadvantages of 3-Tier Architecture in Web Development

A 3-Tier Architecture (3TA) is traditionally used when building web applications. It makes a logical separation between the presentation layer, the business logic layer, and the database layer.

The main advantage of 3 tier system is that all business logic can be defined once within the business layer and then shared by any number of components within the presentation layer. Any changes to business rules can therefore be made in one place and be instantly available throughout the whole application.
It is possible to change the contents of any one of tiers (layers) without having to make corresponding changes in any of the others
Enables parallel development of the different tiers of the application.
Complex application rules easy to implement in application server. Easy to implement changes
Fewer JavaScript, thus simpler to the client
Superior performance for medium to high volume environments

Some of the disadvantages are;
There is more processing on the web server,
It does not interact with the WMS server directly.
More complex structure
More difficult to setup and maintain The physical separation of application servers containing business logic functions and database servers containing databases may moderately affect performance

References:
Sheriff, D. Paul. (April 2002). Designing a .NET Application. [Online]. Microsoft Developer Network.Available from:http://msdn2.microsoft.com/en-us/library/ms973829.aspx [Accessed 17/11/07].
Chapple, Mike. (2007). Two-Tier or n-Tier? [Online].About.com:Databases. Available from:http://databases.about.com/od/specificproducts/a/architecture.htm [Accessed 17/11/07].