I recently needed to convince a client not to build an application in Excel and deploy throughout Europe on CD. To do this i provided the following list of advantages of web applications.

No need for an install or to ship updates

The application lives in the cloud and is centrally managed, when you launch the application you will always have the latest version. This leads to a single point for updates and fixes with the user receiving the updated version the next time they use the application. You remove any chance of legacy applications being used

No admin rights or approval required

There is no software install, which means that as long as the user can access the site they can use the application. There is no need for a network administrator to approve the installation.

Anytime, Anyplace, no distribution network

You don’t have to be on your office computer to access the application, you can use it from any computer with an Internet connection. Which also means you can distribute globally for zero cost.

Build Once, Run Anywhere (Platform independent)

The browser becomes the platform and developing for that allows users of any underlying operating systems (Mac, Linux, Windows) to access the application.

More Robust and Faster to fix

Developing for one platform reduces the risk of environmental bugs. Also even when a bug does get found it can quickly be rectified and deployed to all users see (No need to install of to ship updates). Makes maintenance and support simpler.

Enables social functionality

The world is becoming more social and people want to collaborate and work online together, having a web application allows you to add this functionality.

Lower cost of deployment

No boxes, printed manual, expensive shipping costs, CD’s, distribution channels,etc.

Usable from inexpensive computers

If your user base has a variety of hardware of differing specification then a web application is for you. The browser is very lightweight in computing power terms and your application will run just as well on a Net-book.

Piracy-proof

can’t be cloned in a DVD Writer.

Instant payment, no need to invoice

If you are charging for you application payments are simple, they can be collected through the application so as long as the customer pays, the account is active

No Viruses

No installation, means no viruses.

Simpler mobile deployment

If you decide you require a mobile version you get a high degree of application re-use; re-purpose key functionality via an alternate interface i.e mobile.

Widest potential audience

For all the points above, this basically unlocks markets for software vendors that previously were inaccessible due to technical reasons.

Make use of a users existing knowledge

It’s safe to assume that nearly everyone is familiar with a web-browser and your application can be designed to take advantage of this knowledge i,e forward, back buttons and bookmarking.