It’s incredibly useful to have students work with a partner, rather than doing exercises alone. They start discussing approaches and ideas and have to explain their thinking to each other. This forces them to consider whether their approach is valid, and the act of talking about what they are thinking deepens their understanding as well. Bouncing ideas off of each other leads to further ideas, that would not have come about.
The most fun sessions are when the room is noisy with conversations between pairs of students, conversations across the entire class, students taking hints from each other, offering solutions to solving particularly knotty problems and egging each other on. And most times, we end up with solutions very different from what I had come up with — which is brilliant!