What is the purpose of waffle irons that flip?
Some waffle irons flip to evenly spread the batter. This is important in commercial applications where the visual presentation of the product is crucial and can save on batter - you can use less batter to get a thick, complete waffle. 

The waffle iron presses rely on the expansion of the batter to create a complete waffle. Sometimes in order to get a full, thick waffle, you have to use a little more batter, which often ends up spilling over to the side. It's a trade-off - if you don't want spills, use less batter with the potential for a slightly incomplete waffle.'

From eBay's Waffle Maker Buying Guide - "This ensures even cooking, and it ensures that batter is evenly distributed. There's less risk of ending up with a waffle that has holes."