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.C1List.ListBase.C1ListBase.WillChangeToIndex, which refers to the new selected index.
The WillChangeToText property returns an empty string when the C1.Win.C1List.ListBase.C1ListBase.WillChangeToIndex property is set to -1.