While one-on-one interviews still have a place, gathering a group of individuals interested in becoming a part of the company creates a unique atmosphere and allows personalities to emerge in a more natural environment.
By observing a group and the interactions, the energy of the room can be seen and felt. This is an important indicator of a prospect's success if selected to become a part of the team.
Managers, directors, and team members can observe important soft skills and remove the layer of formalities that accompany one-on-one interviews.
The group environment offers chance to watch someone navigate an unfamiliar situation in a way that feels intuitive as opposed to how it "should" be navigated.