Only when in 4wd. Most people never use it the high majority of the time.
When it comes to great break in, they need to cycle on the pattern where the become work hardened. Remember, there is a phosphate coating that wears off during break in. The temperatures get very high during this process. If you don't believe me, try holding your hand on the pumpkin immediately following your first break in cycle. You might be able to hold it the for one or two seconds. It's slightly cooler the second time. After the break in process is complete, do it again and you'll find that you can hold your hand there no problem I'm most cases.
Breaking in the front gears has differing opinions. In general, the will passively break in and most people would never know the difference since they rarely get used. If you wanted to do it and apply the same concept to the rear, then drop the rear dive shaft and go on a drive in 4 high. I've done that and it made me feel better but I can't say that it mattered because I've also installed a front R&P and the break in period was on a tough trail. Thinking about it now, I did have a front R&P failure on a different trail but I can't attribute it to the break in process. Who knows.
I had an extensive talk with Matt at Revolution Gear and Axle about the break in process as I was getting ready to make a video on it. A lot of good conversation.
With all that being said, my advice is to follow the manufacturers recommendation for break in. You CAN tell a gear set that hasn't been broken in properly. The heat generated is the issue. That's why everything is a gentle drive the first two cycles with no towing.
Here's the video I made for the gear break in process.
