I want to ask if there is a best practice for setting Effect parameters in XNA. Or in other words, what exactly happens when I call pass.Apply(). I can imagine multiple scenarios:

1. Each time Apply is called, all effect parameters are transferred to the GPU and therefor it has no real influence how often I set a parameter.
2. Each time Apply is called, only the parameters that got reset are transferred. So caching Set-operations that don't actually set a new value should be avoided.
3. Each time Apply is called, only the parameters that got changed are transferred. So caching Set-operations is useless.
4. This whole questions is bootless because no one of the mentions ways has any noteworthy impact on game performance.

So the final question: Is it useful to implement some caching of set operation like:

private Matrix _world;
public Matrix World
{
    get{ return _world; }
    set 
    {
        if (value == world) return;
        _effect.Parameters["xWorld"].SetValue(value);
        _world = value;
    }
}

Thanking you in anticipation.