I'm not sure what is meant here, either. It isn't a fixed term- I presume it means activities involving the group where there is an element of competition, which can push students to strive harder. It can help students, though there are other factors, like age which might affect this- I don't particularly enjoy group activities and don't enjoy taking part in them when I'm on training courses. It also matters how well the group know each other and cultural differences.
Group work, when it goes well, works very well, but if it goes wrong can be disastrous. Where are you from, BTW, and your students? ;-)