A cross-platform panacea?

For the most part, Xamarin.Forms defines its abstractions with a focus on areas of the mobile user interface that are common to the iOS, Android, and Windows Runtime APIs. These Xamarin.Forms visual objects are mapped to platform-specific objects, but Xamarin.Forms has tended to avoid implementing anything that is unique to a particular platform.

For this reason, despite the enormous help that Xamarin.Forms can offer in creating platform- independent applications, it is not a complete replacement for native API programming. If your application relies heavily on native API features such as particular types of controls or widgets, then you might want to stick with Xamarin.iOS, Xamarin.Android, and the native Windows Phone API.
You’ll probably also want to stick with the native APIs for applications that require vector graphics or complex touch interaction. The current version of Xamarin.Forms is not quite ready for these scenarios.

On the other hand, Xamarin.Forms is great for prototyping or making a quick proof-of-concept application. And after you’ve done that, you might just find that you can continue using Xamarin.Forms features to build the entire application. Xamarin.Forms is ideal for line-of-business applications.

Even if you begin building an application with Xamarin.Forms and then implement major parts of it with platform APIs, you’re doing so within a framework that allows you to share code and that offers structured ways to make platform-specific visuals.

Source of Information : Creating Mobile Apps with Xamarin.Forms