As you grow more experienced with app development, it will fall on you to maintain older software like Silverlight or help manage local, infrastructure or cloud databases.
Installing the Silverlight SDKs and the LightSwitch tool take up little room on your harddrive, and you might find opportunity to use them. For instances Silverlight is still used by Netflix's and I am sure if you had an opportunity to live in Santa Monica you would take it. As to databases, even app developers are often given the responsibility to implement and maintain databases, in this case LightSwitch is a great tool to do this.
So for Silverlight SDKS and why they are used see: Sliverlight , and indeed Silverlight is fading along with XNA, but you might find the occasional project that is being maintained using Silverlight. Otherwise I am not commenting on Silverlight versus HTML 5, you decide.
As to LightSwitch, well different story here. The development team has been working hard to build out tools for rapidly building and deploying apps that will work on Phone as well as clients. For more information about this see: Announcing LightSwitch in Visual Studio 2013 Preview and Visual Studio LightSwitch .
What does LightSwitch have to do with C++?
As shown in the image, LightSwitch applications are designed using the classical three tier system. The middle tier can be any language, and now that C++ is so much easier to work with, it comes back into consideration.