RemMod1100

Based on my experience (raised 2 GSP's from pups, trained them myself), and as you can see I don't claim to be a pro, I'd put the collar away until the dog is 2 years old. My two dogs couldn't have done a better job their first year in the field. I had spend a lot of time in the yard with a check cord reinforcing sit, stay, come. Out to a year old I think they still are dependent on you for what they are doing and don't range far. Once they hit adolescence (remember the old 1 dog year is 7 human years? Well, that makes a 2 year old a teenager) they think they've got it figured out and don't need you anymore. This is where a collar helps to reinforce in the field what they learned in the yard. I, too, have only used a collar to bring them back. As a friend of my says, sometimes you have to turn their hearing aid on. By the way, hunted with a 6 month old sired by my dog this morning. My friend has done a great job teaching him the basics (come, sit, stay) and the pup did great. Had 3 hard points on roosters and stayed steady to wing. Like I said, we'll hunt him again next season without a collar while he gets it all figured out. I think it's very important for a young dog to thoroughly enjoy himself starting out.
I screwed up hunting my lab when he was 6 months old. I got him to retrieve a bird and bring it to me, but after I took the bird he jumped up on me with his front legs trying to get the bird again and put a nice scratch on my gun. I slapped his nose and told him NO! To this day, and he is 3 now, I cannot get him to retrieve to hand. He comes within about 5 ft., sits, and puts the bird on the ground. I praise him and praise him and leave it be. I know I'm the one that screwed him up when he was young. Lessons learned!!