We talked about various Height and Width such as DesignHeight/DesignWidth, MinWidth/MinHeight, MaxWidth/MaxHeight and Height/Width of WPF Windows and UserControls. They apparently have their own particular use and that is why there are provided.
We just found a practise which we thought as good and would like to share it here. That is, please leave out the Height and Width of UserControl or make them all Auto if possible. It is simple like this. UserControls do not really show themselves directly. Almost all the time, they are hosted in some WPF Windows, WPF controls such as Grid and ListBox, or even some other UserControls. So, it looks good to control the UserControl Height and Width in its host, e.g. setting up the Grid Height and Width there and letting its children automatically fill up, instead of in the control itself since it can not expect all different usage situations to hard code its Height and Width from the very start.
In terms of at design time in Visual Studio, the DesignWidth and DesignHeight are designed right for that situation.