Does unsafe code have any effect on safe code?

Question

As I understand it, marking an method as unsafe will disable some of the CLR checks on that code, but does this have any effect on the rest of the system which is safe, other than the fact that the DLL/EXE can not run in a untrusted environment.

In particular,

1. Are they are any safety checks that will not work on the complete dll because it is marked as unsafe?
2. If a DLL is marked as unsafe, but the methods marked as unsafe are not actually called, is this the same as if the DLL is marked as safe?
3. Are they any run-time benefits on keeping the unsafe code in a separate DLL?

I have the problem with redrawing nested controls on 64-bit windows as detailed here and the one the solutions (the one that appears to work) involves unsafe code and I would like to understand the effect that adding this code has to my project.

Answer 1

An unsafe code is capable of corrupting the managed heap. As such, anything that runs in the same process can be affected.

This includes all other libraries and potentially all other AppDomains in the same process.

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UPDATE

Here is an example: http://blogs.msdn.com/b/tess/archive/2006/02/09/net-crash-managed-heap-corruption-calling-unmanaged-code.aspx

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UPDATE 2

Is unsafe code that is written diligently bad?

No. There are tons of unsafe code in the .NET framework itself. Examples many, but here is one in the System.String:

public static unsafe string Copy(string str)
{
    if (str == null)
    {
        throw new ArgumentNullException("str");
    }
    int length = str.Length;
    string str2 = FastAllocateString(length);
    fixed (char* chRef = &str2.m_firstChar)
    {
        fixed (char* chRef2 = &str.m_firstChar)
        {
            wstrcpyPtrAligned(chRef, chRef2, length);
        }
    }
    return str2;
}