Use of VsHost.exe

What is "vshost"?
This is the "hosting process". It is created whenever you build a project in the Visual Studio 2005 IDE. Its purpose is to provide support for improved F5 performance, partial trust debugging, and design time expression evaluation.
Should I deploy the "vshost" files with my application?
No. The "*.vshost.exe" and "*.vshost.exe.config" files are only for use in the Visual Studio 2005 IDE. They should never be run directly, and they shouldn't be deployed with your application.
The hosting process is a feature in Visual Studio 2010 that improves debugging performance, enables partial trust debugging, and enables design time expression evaluation. The hosting process files contain vshost in the file name and are placed in the output folder of your project.

Hosting process files (.vshost.exe) are for use by Visual Studio and should not be run directly or deployed with your application.

Improved Debugging Performance

The hosting process creates an application domain and associates the debugger with the application. Performing these tasks can introduce a noticeable delay between the time debugging is started and the time the application begins running. The hosting process helps increase performance by creating the application domain and associating the debugger in the background, and saving the application domain and debugger state between runs of the application. For more information on application domains, see Application Domains.

Partial Trust Debugging

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An application can be specified as a partial trust application in the Security page of the Project Designer. Debugging a partial trust application requires special initialization of the application domain. This initialization is handled by the hosting process.

Design-Time Expression Evaluation

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Design-time expression evaluation enables you to test code from the Immediate window without having to run the application. The hosting process executes this code during design time expression evaluation. For more information, see Immediate Window.

http://msdn.microsoft.com/en-us/library/ms242202.aspx