I'd fit in this category. I'm a company executive and I have a voice that carries. I tend to be the quiet person in the room until I need to speak up. When I do, a mix of my position, and the whole quiet-person-speaking-forcefully thing tends to make others listen.
In general, I don't mind being in front of a room, giving a presentation to 2000 strangers. The faces blur together and it's like being alone. Because I'm willing to do this, many people think I'm an extrovert. On the other hand, I don't like being in a room with 4 strangers. I can do it, and I'll interact with everyone, but it is freaking exhausting.
Anytime I'm with people for a decent length of time, I need time alone to recover. A large part of my job is managing or dealing with people for one thing or another. It's become a habit that when I get home from work, my family leaves me alone for an hour so that I can decompress and recharge.
They are a middleman and do take a slight overhead, 1.1% last I saw, though it might have changed since then. The benefit is one of simplicity. Many people want to give to charity and aren't sure which one. UW let's them donate one place and it get distributed to many. They also have criteria that charities must meet to qualify. Also, like you mentioned, they do the paycheck deduction. All of what they do is about making it easier and hassle free as possible to donate, making it more likely that people will.