This is actually an old topic; however, I need to provide this information for my work. So I decided to do a quick research again and put the benefits of using web application together.
There we go. Here are the benefits.

• Easy deployment
• Doesn't require client installation.
• Once server gets upgraded, all clients can enjoy the newer version of the software. The traditional applications need to be exclusively accessed during upgrade process which makes them hard to be upgrade especially in terminal service environment. Web application can be upgraded even when the client still using the previous version.
• Unified client
• Web application clients are web browsers which are normally equipped within OS. There is no special requirement installation for clients. On the other hand traditional application sometimes requires some special runtime to be installed on the client machine.
• No continues connection
• Web clients only connect to the server when they need to send or receive data from server. No continues connections means server does not need to maintain the connection status which implies less load and better performance for the server.
• Easy fail over
• Web application only holds the business logic. It should not have any data. If the web server goes down, we can easily setup another web server and redirecting the request through DNS settings.
• Same security threat as traditional window application
• Web application does not necessary mean its public to everyone on the internal. It can be totally internal just like the traditional application.
• Performance
• Same as all network applications, web applications are limited by network bandwidth. It does have a little bit overhead in data because it needs to transfer the client presentation information. However, the overall bandwidth usage should have not much difference compared with traditional application. Furthermore, the newer web application technique, AJAX, can reduce the frequency of transferring presentation information. As a result, there is almost no difference in bandwidth usage between web application and traditional application.

In summary, there is not much difference between traditional application and web application in many ways; however, web applications have one major advantage, easy deployment, which traditional application does not.