I use treats to encourage an enthusiastic heel. Sometimes I want a calm heel and other times a "drivey" one. Treats can build drive.
I use treats on recall. I want my dog to know that coming to me is the best thing ever. On walks in the park early in the morning, he is off leash with an e-collar. When I call his name, he gets a treat when he comes back to me. Then, I usually say "break" and let him go freely again. If he voluntarily comes back without me calling while on the walk, I also give him a treat. He is 2.5 years old. I have been treating a recall (casual or formal) since he was a puppy. A recall is a most valuable command to have rock solid. E-collars are excellent tools, so are treats.