I think group work or pair work that focuses on a grammar target structure is useful. The best thing to do is wait until you get there, and figure out the best thing to do. Every situation is different. I've learned to not listen to anyone regarding this. Find out for yourself. A few mistakes I've made have come from taking into account what someone told me before the start of a course or lessons. It's not very fashionable to admit to making mistakes thought, is it?