I think you may be talking about shifting food and recruits from tc to tc. That can be beneficial if you are full of food or recruits and want to store it for later. Typically you would have something like 3 TCs running at ultra low cost and one running at legendary. Since legendary takes a lot of food and recruits, it can be stored there and removed later. There isn’t a way to shift stored heroes if they’ve already been trained. If you click on the icon, it will collect them and place them on your hero roster.