A WPF browser project is the same as writing a java applet/application, only you use IE and .net instead. you would do it for the same reasons you would write a java application.
The main wpf cons are:
- User must have .net installed, and use IE to access the app.
- Slow load time (.net vm must be loaded and app jit'd)
the main wpf pros:
- Rich UI (winforms)
- Coding understood by windows programers
the main asp.net cons:
- Programmer must learn web model
- Somewhat limited UI
- Cross browser testing required
the main asp.net pros:
- Cross browser compatiability (universal access)