Basically it is a way within the sim to simulate "periods" of WW2 aviation. As we all know, WW2 saw huge advancements in military aviation in a shirt time. The kites that saw action in the Battle of Britian were, in many cases, VASTLY inferior to those who saw action in mid 1945. The point of the rps is to allow the players to enjoy combat from all eras, and not limit it one era. In AH, that is 1945.
In WB's, there was a LOT of debate when it first got introduced after 2.0 came out. I for one loved it!
Strider 417