Most of us re-gear as a way to bring our gearing back to stock or better than stock when going to larger tires.
When I started wheeling in 2003 and went to larger tires I chose not to regear my diffs as I figured 4.30's we plenty low for what I could handle.
Over time, I modded my truck, I got more brave, I burnt a few clutches, and I decided 4.30's were not low enough for the trails I was running but they seemed like a nice compromise of fuel economy and power for the street so I added an Ultimate Crawler. I had the best of both worlds, fuel economy on the street and low-low gearing for the trail.
Well, that all sounds well and good...
October 2006, while wheeling in Moab, UT I broke 5 teeth off of my rear ring gear and destroyed the pinion (approx. 100k miles on the diff). I u-hauled home and fixed my truck with a used rear diff from a junkyard (approx. 100k miles on the diff). I actually broke the front ring and pinion too, but that's a different story.
March 2007, while wheeling in Farmington, NM I broke 3 teeth off of my ring gear. I limped home in front wheel drive (rear drive shaft removed).
I can't figure out why I am breaking diffs...I have to build a stronger one. I am curious about Cryo-treatment. Steve at Sonoran Steel informed me that Bobby Long will Cryo gears. I call Bobby and explain the situation. He tells me that he thinks I am breaking parts due to the extreme power from the crawler and the deflection of the gears since I am running diffs with a lot of miles on them. I trust an industry legend like Bobby Long to diagnose the issue.
Long story short....if you have re-geared you have probably avoided this issue since your diff has been re-set. If you don't re-gear at least have your side bearings tightened and check your back lash to reduce the deflection caused when things wear naturally over time.
My solution
Short Term: I bought a new OEM diff, it's in and running smooth.
Long Term: I have a set of gears a Bobby Longs getting Cryo'd. I will build a bullet proof rear diff and keep the new OEM for a spare. I am not going to miss a day of wheeling due to a broken rear diff again.