Jeff:
I'd say three ways:
1. It's a bit of market research on what people who are interested in golf architecture would like to see. But, it's not really a great source of feedback ... with certain exceptions, we'd get a lot more feedback about our own courses by actually going there for a day and asking the customers.
2. It's a sounding board for new ideas.
3. It's an ego boost. Every architect who participates here has a higher profile on GCA than they do in real life, whether they are a busy architect who's not a household name, a starting architect who's trying to find a voice, or even (as Mike Y. points out) a quasi-architect who's pretending to be a real one. I suspect this would be true even if every architect in the world participated, because there are more fans of golf architecture here than anywhere else I can think of.