The act of bidding itself shows interest and raises the price.

The act of viewing the item page in itself demonstrates activity and is relayed to other users; leaking information about, not necessarily intent, but awareness. If you want something, figure out the details without actually clicking on it.

Auto bid raises the price to the second highest price among auto bidders, basically running an instant second-price auction. Sniping avoids running these pre-close auctions.