There is a very simple application that I (probably) need to make. When I heard the requirement, I immediately thought about making an online / web application, though the customer apparently had the desktop application in mind. q1. When is it necessary to write a desktop application? q2. I'm just thinking that I can install a web server and also possibly a server side script like php to set up this online / web application, but what are downsides? What are limitations ...?
When it is a big application with lots of features, and has no need to be online. Big web applications suck to those with slow connections.
If the customer wants a desktop app, give him what he wants. I'd add to blueparukia's comments that a desktop app is needed if the user wants to save files onto his own hard drive and not onto a remote server.
Not that you couldnt install a web server on the client machine and have the 'remote server' actually be the localhost. But yeah, the other guys are right: unless you have a good reason to disagree, if they ask for a desktop app, give them a desktop app.
An interesting (and very valid) viewpoint. I did this myself a couple of years ago. I ran a web app on the desktop and used TCP/IP to communicate between components. I did it so that elements of the app could be run on the web and different types of use could have the same UI/ experience. This approach isn't to be discounted.
Well, you considered making an application using PHP. PHP does scripting, ASP.NET does applications. And very easy too. You can port any desktop application to the web using ASPx and vice-versa. It's good to have a web application because it's accessible everywhere you have an internet connection, and you don't need to install anything.
Depends what programming you know. For example, you could go with Java and use the same code with a bit of tweaking on a website and on your desktop. So it depends on what you know.