I will list the ones I found so far.
- extensibility. You can add a new xml in order to add new columns.
- configuration over code. Less code for logic, more declarative xmls.
- less traffic over the network. The xml is transformed into a json and sent to the browser. Also each field type is sent only once to the browser and the form generation happens on the client.
- the new system allows column reordering and state saving.
Off topic: I got "inside info" that the plan is to move all the grids and forms to UI components. So you should start using them.
