Web applications are applications that allow a user to interact with them over the Web. All the overhead is absorbed by the server and the client does not need to worry about installing, upgrading, or maintaining the application. Advantages Web applications are inherently platform independent. Many users do not have the time to download an application and install it, to evaluate it or get the new version every time it is released. They prefer to stick with the older version even if the newer version offers more features.
Web applications upgrade themselves transparently to the users.
The developer can install, apply patches, or upgrade the application at the server and all the client users will immediately benefit from the changes without any effort on their part. When developers design a new application, or add a new feature to an existing application they what to know how many users actually use it. With traditional applications, they can look at the number of sales and see how many people actually purchase the software. However, the number of sales does not tell them how many times each person use the software. Web applications allow per usages accounting.