This property will most likely be used during SelChange event, and it will give you the text of the new selected item. It is related to C1.Win.List.ListBase.C1ListBase.WillChangeToIndex, which refers to the new selected index.
The WillChangeToText property returns an empty string when the C1.Win.List.ListBase.C1ListBase.WillChangeToIndex property is set to -1.