Maybe if you were hatching in a very fancy incubator with tons of eggs and a medical grade thermometer while trying to get exact results for a study or similar. The actual temp you can incubate eggs ranges from 98 to 102 with some people even going outside of that. A still air should be run at 101-102 and a forced air 99-100 on average. However then there's the fact most people don't have extremely accurate thermometers so they are probably off by as much as a degree and occasionally a few degrees. By the time you get done with all the variables there's no reason to lower the temp for 99% of the people hatching and probably not even for commercial hatcheries. Eggs will still incubate and hatch in a range of temps. Just adjust the temp based on when they hatch. If they go a little early lower it and if they go a little late raise it. Attempts to change a temp that's working fine may just throw your incubator off and kill everything when it seems completely unnecessary. That's the first thing I've seen that says you should change the temp for hatching.