Why should you remove unnecessary C# using directi

Question

For example, I rarely need:

using System.Text;

but it's always there by default. I assume the application will use more memory if your code contains unnecessary using directives. But is there anything else I should be aware of?

Also, does it make any difference whatsoever if the same using directive is used in only one file vs. most/all files?

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Edit: Note that this question is not about the unrelated concept called a using statement, designed to help one manage resources by ensuring that when an object goes out of scope, its IDisposable.Dispose method is called. See Uses of "using" in C#.

Answer 1

It’s personal preference mainly. I clean them up myself (Resharper does a good job of telling me when there’s unneeded using statements).

One could say that it might decrease the time to compile, but with computer and compiler speeds these days it just wouldn’t make any perceptible impact.

Answer 2

Having only the namespaces that you actually use allows you to keep your code documented.

You can easily find what parts of your code are calling one another by any search tool.

If you have unused namespaces this means nothing, when running a search.

I'm working on cleaning up namespaces now, because I'm constantly asked what parts of the application are accessing the same data one way or another.

I know which parts are accessing data each way due to the data access being separated by namespaces e.g. directly through a database and in-directly through a web service.

I can't think of a simpler way to do this all at once.

If you just want your code to be a black box (to the developers), then yes it doesn't matter. But if you need to maintain it over time it is valuable documentation like all other code.