Mike, there are times where you do HAVE to cut the eggs.
1. If you substrate was to moist and your at the final day when the egg is due to hatch and they are still VERY full the baby can have issues cutting out and can drawn in the egg.
2. If the egg is small because its 50 or 60% "boobed" and thus the baby is very small if they are trying to cut into the almost calcified "boobed" portion you could loose them
3. If you develop mold on the egg or large windows because the egg gets wet. My favorite way to fix the egg is with Children's elmers glue. Putting the glue on the mold suffocates the mold and will seal a window up. The babies cannot cut threw the glue and may need help out.