The purpose- as with any cooked meat- is to let the meat firm up so it doesn't release juices when you cut into it.
In the case of a turkey it also helps to let it cool enough to not burn you when you are carving and eating it.
Both of these goals will be met in 30 minutes to an hour.
I don't know why that chef would recommend 3 hours.
At that length of time the turkey would start to approach room temperature and would be less appealing to eat as well as start the clock on the danger zone.
cooking.stackexchange.com/users/2001/Sobachatina
I heard GR say 3 hours this year too, so you're not misremembering.
I recently started letting it rest for 45 minutes to an hour, and it's worked out great.
My reason for choosing that amount of time is: that's how long veggies need to roast in the oven.
Once upon a time I used to rest it for 30 min, meaning I needed to at least start roasting the veg while the turkey was still in the oven, and the whole thing was insanely stressful.
Now I prep the veggies but put them dry on baking sheets.
An hour before I want to eat, or when the turkey is clearly cooked if that happens sooner than I expected, I pull out the bird and get it out of the roasting pan and onto a tray to rest with foil over it.
I put the fat and juices from the roasting pan into a measuring cup to settle, and get the fat spooned over the potatoes and in they go.
Get the stuffing out of the bird, squash (cut in 8ths or 16ths and buttered) into the oven and the cranberry sauce on the stove, that typically takes 15 minutes, so it's time for parsnips and onions to go into the oven again with some of the turkey fat.
Then make gravy in the roasting pan using the not-the-fat part of the settled juices and cook the Brussels sprouts on the stovetop.
More room, less panicking, and as long as you understand you will not have a single pause during the final hour, much easier than it used to be.
We have had no consequences of resting it for up to an hour, and I don't see any purpose in resting it longer.
cooking.stackexchange.com/users/304/Kate Gregory
I've been letting my turkey rest for over 2-3 hours for a couple years now because of this advice from Gordon.
It's amazing!
I cover with tin foil
and then a couple of towels to rest
and the bird is still PIPING hot hours later.
I'm usually cooking a 25 pounder.
The internal temperature actually first goes UP to 180 then settles back to 150 by serving time.
There's no safety risk here.
You can then have everything done, pots and pans washed and enjoy a beautiful dinner
cooking.stackexchange.com/users/40259/Carol
I have carved within 20 minutes and within 3 hours.
I strongly believe that the longer standing time has created the most outstanding and moist, delicious turkey ever.
I have cooked
20-25 lb Turkey's stuffed and unstuffed every Xmas and thanksgiving and have never had a negative result from resting either way.
Don't be afraid to try something new.
Make sure your turkey is always properly covered with foil when resting and more importantly clean as you go and make sure the raw handling is properly followed by a thorough cleaning with disinfectant wipes or hot soapy wipe ups.
Some folks like well done meats and some like moist juicy meats at the optimum temperature.
Either way, enjoy your turkey and company and make the day fun and not a chore:)
cooking.stackexchange.com/users/22358/Johnny boy
A 20-25 pound turkey having roasted for hours will continue to have rising internal temperatures, and will be too hot to safely handle and carve immediately.
While waiting three hours to commence carving is more patience than I can muster, I try to let it rest at least one hour after pulling from the oven, and have outstanding results.
My family has not eaten dried out turkey in many, many years.
cooking.stackexchange.com/users/52270/Kevin
It's to let the juices get absorbed into the meat.
The meat doesn't have to be piping hot, as the gravy will be.
It's common knowledge to let the turkey rest for around at least 2 hours.
It will completely enhance the taste.
cooking.stackexchange.com/users/14796/Gordon
I have been cooking my entire life and owned restaurants in the past, and I have never let a turkey rest over one hour.
cooking.stackexchange.com/users/22142/Timothy
We went to a cooking school last night, and both chefs recommended letting the turkey rest for 3 hours.
cooking.stackexchange.com/users/29444/jane Carney
It all depends on how you wrap it for resting.
I did exactly what GR suggested.
I smoked it for 3.5 hours and got the internal temp to 165.
Pulled and placed in an aluminum pan, covered with aluminum foil, wrapped all of that in towels and placed all of that in an ice chest.
3.5 hours later I had the best turkey I have ever eaten and it was still steamy hot.
It was even better than fried turkey.
cooking.stackexchange.com/users/29592/user29592
I only researched this to verify that it was ok to leave my sixteen lb bird out for three hrs after cooking for three hrs.
I was very paranoid that someone would get sick.
Apparently it is ok.
I was so concerned that I don't even care about juiciness, flavor or any other etc.
I cook two birds and with everything else going on
I just had no time to deal with the first bird after it was done.
Today almost feel like I dodged a disaster.
cooking.stackexchange.com/users/41158/Laurie Quinn
I cooked one FRESH turkey at 17 min a lb for 4.5 hours.
Took it out and tented it.
It rested for 4 hours like Gordon said and it was still way above danger zone temp.
It takes a long time for those things to cool down man.
BTW Best turkey I ever had.
Remember to pull the stuffing out first.
cooking.stackexchange.com/users/41901/Chriscc22
I have heard mixed advice on how long you should let a turkey rest after cooking.    Last year my wife and I watched a Thanksgiving cooking show with Gordon Ramsey and he said you should let the turkey rest for as long as you cooked it.  If you cook it 3 hours, it should rest for 3 hours.  That seems like an awful long time to me.    Everything else I've read looks like 30 minutes to an hour is fine.  Any suggestions?
How long do you let a turkey rest after cooking?
cooking.stackexchange.com
<turkey><thanksgiving>
cooking.stackexchange.com/questions/19012
cooking.stackexchange.com/users/5415/Shawn Steward
Depending on how you wrap it for resting, the internal temperature should continue to rise and it will still be hot after two or three hours when ready to serve. This will produce a moist, delicious turkey, but resting for an hour or less will also produce good results. Some people think that resting for over an hour is unnecessary, however others say that the turkey will still be sufficiently hot to eat over 3 hours later.
45 to one hour is more than enough. The bird will still be hot hours later. After 3 hours resting, the internal temperature remains at 165°F.