MethodImpl(NoOptimization) on this method, what does it do? And is it really nessecary?

Well, I wanted to hash a password, and i had a look at how ASP.net Identity does in the Microsoft.AspNet.Identity.Crypto Class, and i came along this function (which is used to compare the 2 password Hashes):

[MethodImpl(MethodImplOptions.NoOptimization)]
private static bool ByteArraysEqual(byte[] a, byte[] b)
{
    if (object.ReferenceEquals(a, b))
    {
        return true;
    }
    if (((a == null) || (b == null)) || (a.Length != b.Length))
    {
        return false;
    }
    bool flag = true;
    for (int i = 0; i < a.Length; i++)
    {
        flag &= a[i] == b[i];
    }
    return flag;
}

This is a direct copy from the reflector output...

Now my question is, what is the NoOptimization attribute good for, and why should it be there(what would happen if i remove it)? To me, it looks like a default Equals() implementation until the for-loop.

I tried to have a look at the IL but it is all nonsense to me :/