The IP stands for "Initial and Pitch" - as in fly the initial leg of a circuit, then bank the aircraft and pitch onto the downwind in a constant turn. In it's simplest form it is basically an upwind join.
It is designed to allow a flight to maintin their formation to the circuit, then space the individual elements out for separate landings.
In the "old piston days" in Europe, it allowed an aircraft to maintain energy right to the airfield, then rapidly bleed that energy off in a high G turn onto downwind for landing - giving minimum exposure to the low energy state where the aircraft is most vulnerable to attack.
Neither situation really applies to civil operations, where flexibility in entering the circuit is more important and efficient in handling traffic.
That doesn't mean that it isn't fun though
[ 13 November 2001: Message edited by: Checkboard ]