This is a good article explaining a bit about why targeting and other simple skills are helpful for reactive dogs, and it touches on how positive reinforcement plays a part in training/re-conditioning them to the behaviours and responses we want them to demonstrate. For most dogs that positive reinforcement is food, but positive reinforcement is simply what motivates your dog the most-something they really love. For my big dog it is food and different foods have higher values than others. I use them for the really difficult environments and new skills. For my little dog, the best thing ever is actually a quick game of tug or fetch.