Unused reference assemblies are removed by the compiler.
Create a new console application in VS and it will be used by default for multiple builds. Compile your empty program and open it in the reflector, and you will see that it refers only to mscorlib. The rest are deleted.
The same applies to unused using statements. The compiler deletes them.
You might want to remove unused links and use them to maintain cleanliness and readability.
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