I thought it was called a Direct Vision window because you could look through it and land the plane if the windscreen misted or froze up. (thats what my instructor told me) It gives you one more chance of landing if it all goes pears.
Obviously this would require some side slip and craning of the neck in the piper versions. Must try it next time.
Didn't someone who got a windscreen full of oil on take off use it to land the plane at Barton some 10 ish years ago.
I also recall stories of glider pilots getting frozen canopies in flight necessitating the use of the DV panel to land.
Anyway whether or not its true it sounds better than a clear prop window.