Charity Without the Events

There's something I've been thinking about for a few years now. It started back in undergrad when some friends helped with the Race for the Cure (or some similar breast cancer thing). They raised a lot of money and had a big walk/jog event and it was very emotional and uplifting. Since then, I've noticed something about charity groups - people want something tangible from their donation.

I've wondered why people need an event or something to give money to a group. A friend of mine works with a group called St. Baldricks. It's a group that raises money for childhood cancer research. It's an organization with a great mission. The group members raise money and after collecting it, shave their heads in "solidarity" with the kids with cancer. Why can't all the money go directly to research without the big event? I understand solidarity with cancer patients, but I have to wonder how much more money would be sent to research if the events were not held in the first place?

If I had more time, I'd like to see the comparison between groups who host big events (e.g. Race for the Cure or St. Baldricks) and groups that don't host big events as far as I know (e.g. Heifer International or Bread for the World). Do people give more when they get a big event in return? Just something I've been thinking about for a while.