There is this website (Nees, 2010) shows the advantages of using a desktop application compared to web app (where I agree with his points) which are:
1. Can conveniently run in the background and pop windows or notifications in a friendly mannerHave you seen web apps try to pop windows or notifications? They are not always very user friendly. Gmail chat as a web app tries this. If the browser is in the background, the window title on the task bar changes to show the name of the user that sent you a message. It is a decent attempt at a notification, but if you install a Desktop version of a instant messenger you’re generally used to a more user friendly toast pop.
2. Can offer better usability with more design and layout optionsSometimes you want a more minimalist approach with applications. Say you want an application that will keep track of your stocks for instance. You may not want to have a full browser window or tab open for that information. The Vista or Windows 7 gadgets can provide a minimal view of your stocks. The gadget can conveniently run in the background and consumes fewer resources than a web page. I’ve used a couple browser extensions for a minimalist view, but even those can consume more resources than necessary and I can’t really classify those as a web app.
3. Integrate more seamlessly with other applications and hardware devicesHave you installed Microsoft OCS? How many hooks into other applications does that desktop app have when you install? I open up Outlook and compose an email I’ll see the OCS status next to the contacts name. That integration can only happen through a desktop install. As another example, it is not likely you’ll see a DVD burner web app.
4. Can run standalone without LAN/WAN connectivityIn some environments internet access or perhaps even LAN connectivity is restricted for security purposes. Perhaps it is not restricted, but you want to offer a survivable solution in the event that the LAN/WAN is unavailable. Your primary work might be done offline and then sync’d up later when connected. It is difficult for web apps to function under those conditions.
5. Are more responsive and perform fasterWeb apps inherently carry overhead that comes with a general purpose web browser. Desktop apps can be designed to only load what is needed, which can be considerably less than the memory or other resources consumed by just a base browser startup. Think about the lightest desktop app you use. Would you still use it if it required you to start IE every time or even open a new tab?With new technology web apps are increasing providing functionality we only thought possible in a desktop application a few years ago – who would have thought we’d have a web app version of Photoshop? source: http://www.inin.com/Blog/archive/2010/03/30/top-5-reasons-desktop-apps-are-better-than-web-apps.aspx
I am agree with some of the points which I have highlighted. The reason of creating a desktop application is because it is more user friendly, users just have to install and the program will automatically runs in background until you want to close it or whatever. It will give you notifications like pop-up and alert (for example: MSM Messenger, Skype, etc...) so that you would not have to go to the browser and click on the tab to view the webpage to check while you are doing some other things. Even web apps have notifications, but they will only appear on the title bar of the webpage, so still, it is within the browser itself, and that's one of the limitation of web app.
Beside, it also saves more memory than a web app and it does not always require an internet connection. For example, files that have saved using a desktop application can be easily viewed and navigate even though there is no internet connection, unlike the web app, internet is required can only interact with it. And it is rare possibility for a web app to able to manage different accounts at one time because this required much more memory and space and hence require more time to load. This might leads to dissatisfaction of using the product and eventually reduce the user experience.