There are 2 points I'd like to make:
1. As a seller, I know that starting at a lower price (rather than the reserve price) often gets bidders into a bidding war. If I start an item I expect to sell for $50 at $45, I'll be lucky to get 1 bid. If I start it at $1, I'll usually get 3 or 4 people bidding on it. Their bids get a lot of other bidders to take a second look at the item, enticing some of them to bid also. Often, it will end up selling for more than what I expected if this is the case. Plus, the listing fee is lower if you start the bidding lower.
2. I want what I said in #1 to happen... more interest, and more bids resulting in "auction fever" where people end up paying more than it's actually worth. BUT, as Ausm stated, in small niche markets, there's a chance that only a limited number of people will bid on an item, and I won't get anything near what the item is worth. THAT's when I use Reserve.... as a way to protect myself. And, in these circumstances, I can see nothing wrong with telling a potential buyer what the reserve is, if they ask.
Plus, since you're not alone in selling certain types of items, someone doesn't want to be bidding on your auction with an uncertainty of winning when they can bid on another auction without a minimum. So, by finding out what the reserve is, it assures them that they can win your auction with a bid of what they feel is reasonable.