The "practice with full" theory is one I've tried and abandoned. It's one more thing to think about and the objective is to reduce your variables. If you drop a lot of targets in your practice you might ascribe it to the full choke instead of some other problem such as a poor mount, lifting your head, stopping your gun, etc.
Or let's say you practice with full, crush targets, get pumped up about how easy it will be in competition and then drop an soft pair early in a shoot. Then you start to wonder why because it was supposed to be easier with a more open choke and you are most likely done for the day.
Use the choke that is right for the target.