Do unused usings in .net affect performance? [duplicate]

Answer 1

NO, but It effects the IDE performance and the compilation process of your project. I can give you a short example. If you have ever used coderush http://devexpress.com/Products/Visual_Studio_Add-in/Coding_Assistance/ which is from devexpress, their IDE optimizer and code optimizer will also suggest you to remove unused namespaces.

Update: Here is more use information from Dmitriy's Blog There are few reasons why you should remove unused usings in you C# code.

•It is useless code, that just creates clutter in your source code and it also confusing for the developer because you don’t know which namespaces are actually used.
•Over time as your code changes it can accumulate a lot of unused using statements which create even more clutter in you code.
•It can make your compiling faster, since compiler does not have to look up all those extra unused namespaces.
•It will help avoid name conflict with new items that you going to add to your solution if both of those have same names.
•It will reduce number of items in your Visual Studio editor auto completion

There are couple ways to remove those unused usings, you can do it individually on each file

http://msdn.microsoft.com/en-us/library/bb514115.aspx

You also can download plugin called batchFormat for Visual Studio 2010 that can help you to remove all unused usings for the whole project.

http://www.addictivetips.com/windows-tips/batch-format-remove-unused-usings-and-format-visual-studio-document/

Answer 2

No, they do not. In fact, they have no runtime significance whatsoever, regardless of whether they're used or not. They're just a compile-time constant to allow the compiler to recognize types without specifying their full name explicitly.

Their main problem is that a file full of unused usings forces you to make a pointless PgDn when going over the code.