I was a volunteer firefighter for 28 years. It looks only a little odd when too many response vehicles attend, it looks terrible when too few do! Many times I would take a truck to the scene by myself, and really be hoping for prompt arrival of the next vehicle. And, even if there is nothing to do for most of the responders at a "simple" call, there are training opportunities, and the opportunity for various first responders to renew a sense of teamwork. When I was crashed by my student, I don't know how many vehicles responded, but I sure was happy to see them!