Yes, it is just about performance, although I will need to issue some new guidelines for when it is needed beginning with LV 2012... the LV compiler keeps getting smarter, and it is sometimes hard to keep our "best practices" document up-to-date. For more about this, look at the online help that ships with LabVIEW about the IPE and the "mark as modifier" option. There is discussion about dynamic dispatch VIs specifically.