i'm not sure the actual physiological reason.....but i was told it brings them slowly to room temp and helps settle the air sacs. that way ur not putting them in a warm bator after they've probably reached a kinda cold temp....and they've probably gotten jostled around during shipping.....i heard to let them rest overnight in like an egg carton with the small tip pointed down.
yes you should let the eggs settle by unwrapping them and placing them in an egg carton with the small end down for at least 12 hours but closer to 24 is preferred. The reasoning behind this is b/c during shipping the air sac get jostled pretty good and this time lets all the air bubble that escaped and the air sac return to where and shape it is suppose to be as well as let the eggs come to room temp before putting in the bator. There has a been a few post on here with bad hatch rates and come to find out later they was in a hurry and didnt let them settle. If you are pushed for time b/c of day laid you should let them settle for at least 8 hours.
Thanks for the advice...... they didn't travel far, but I decided to rest them for 4 hours (laid horizontally) so I hope I haven't compromised the hatch, I will let you guys know how I go. Thanks again for your interest