Advantages
- If you are familiar with java. There will be no learning curve
- Code can be reusable + all the facilities come along with java
- When the application becomes larger the code will be easy to maintain
- Handle the browser compatibility
Disadvantages
- Need lot of memory to run it in dev mode
- High compile time
- Every server call will be ajax
- You will loose control on your javascript
That's all i can think of now :-). Find more in http://www.javacodegeeks.com/2012/01/gwt-pros-and-cons.html