Dave Lloyd's 2 Cents

 

For example: 
=iif( me.Value < 0, “Red“, “Black“) placed in the color property of a textbox this expression will change the text colour based on the value returned.
=Format(Fields!BirthDate.Value, "MMM dd,yyyy") placed in the value property this expression will format a date value, (ie Dec 10, 2006)=System.Web.HttpContext.GetGlobalResourceObject("AppResources", "ID14831").ToString() placed in the value property uses your existing resource file to translate a label

Source: Dave Lloyd's 2 Cents