An unused using has no impact to the runtime performance of your application.
It can affect the performance of the IDE and the overall compilation phase. The reason why is that it creates an additional namespace in which name resolution must occur. However these tend to be minor and shouldn't have a noticeable impact on your IDE experience for most scenarios.
It can also affect the performance of evaluating expressions in the debugger for the same reasons.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…