As of Q1 2015, the Telerik® UI for ASP.NET AJAX suite uses the standard .NET licensing mechanism, which means that using the controls in design-time causes Visual Studio to add a license.licx to the solution. This file is used only in design-mode and is not needed for deployment explicitly. The .NET framework (lc.exe) will embed it in the assembly your WebApplication will be built for deployment.
The license file is maintained by Visual Studio and contains information about all licensed components in the application (including non-Telerik products).
Having this license file is not expected to bring any performance/compilation issues and you can ignore it.
In case your project build fails with errors pointing to the license file, you can delete it and rebuild.
Alternatively, you can clear its contents and mark it as
All known errors related to the licenses file usage are covered by the following KB article: How to fix License File related errors.
If you are working under source control, once the file is created, it will be detected as a change by your source control system. We would suggest that you check-in this file initially. Then, when it is checked-out again during your work, it is up to you to decide whether to check it in, or discard the changes.