This maneuver was developed to increase both downwind and upwind performance especially at night.
We all know the difference between sailing close hauled and close reaching. Your most efficient way of getting to an upwind destination is close hauled (45 deg off the wind) . You will move faster close reaching (more than 45 deg off the wind) but you will be going away from your target. So, sheet the jib in tightly and keep the tell tales streaming - easy peezy.
As it becomes dark and you can't see the tell tales, close reaching feels very much the same as sailing close hauled, but it's hard to differentiate whether you're sailing 45 deg or 55 deg off the wind. What we do every 20 minutes is head up until you hear the jib luff then head down 5 deg until it quiets, you will be close hauled- and get there sooner.
On the downwind aspect of the Crazy Ivan, I consider the boat to be on a broad reach when sailing with the wind more than 90 deg off the bow down to where your jib collapses behind the mainsail (about 160 deg off). If your destination is directly downwind, 160 deg off is more advantageous than for example 140 deg off the wind. Like the above, both angles feel the same when it comes to what you "feel" wind-wise (apparent wind). Every five or ten minutes when sailing on a broad reach, "crazy Ivan" the bow downwind until the jib collapses behind the mainsail, then immediately head up until the jib fills. You will now be on a low broad reach giving you your best performance downwind and you'll get there sooner.