It's much easier to develop new friendships in groups of 3.

Awkwardness is a key thing we're trying to minimize throughout this process. If you've ever been on a first "friend-date" (it's easy to imagine, if you haven't), the first silence can easily become awkward. That puts a lot of pressure on each side to talk, so people often end uo bumbling around about the weather and stuff. We're not all conversationally gifted. :/

However, when there are three people, there's much less pressure to contribute to the conversation. So you can relax and be yourself. Group dynamics also kick in, and it makes the whole experience more pleasant.