courtesy Dan Lew for this idea that he gave me on the [fragmented podcast episode #5](http://fragmentedpodcast.com/episodes/4/) (around the 4:30 mark).

`.combineLatest` allows you to monitor the state of multiple observables at once compactly at a single location. The example demonstrated shows how you can use `.combineLatest` to validate a basic form. There are 3 primary inputs for this form to be considered "valid" (an email, a password and a number). The form will turn valid (the text below turns blue :P) once all the inputs are valid. If they are not, an error is shown against the invalid inputs.

We have 3 independent observables that track the text/input changes for each of the form fields (RxAndroid's `WidgetObservable` comes in handy to monitor the text changes). After an event change is noticed from all 3 inputs, the result is "combined" and the form is evaluated for validity.

The value of this technique becomes more apparent when you have more number of input fields in a form. Handling it otherwise with a bunch of booleans makes the code cluttered and kind of difficult to follow. But using `.combineLatest` all that logic is concentrated in a nice compact block of code (I still use booleans but that was to make the example more readable).