Stand mixers make life easier in all too many ways, but I can't stand it when recipes ask you to scrape down the side of their bowls. I'm too impatient to stop and scrape, and am therefore always concerned about getting my spatula or spoon in the way of the whisk attachment or angering the machine somehow. But when baking, there's no question that incorporating the batter fully is key, so I resort to wincing and scraping cautiously. That's where the Beater Blade comes into play.
The Beater Blade is a straightforward stand mixer attachment (most varieties fit KitchenAids, but some fit other brands), and comes in different sizes for different bowls/model types—an important consideration when buying, since a snug fit is key. It screws right on and acts just like a paddle, scraping the edges of the bowl (and the little dimple at the bottom) as it goes around. For about $25 (cost fluctuates based on model, starting at $22), it does exactly what it says it'll do, but the price seems steep for what's really just one function. Though the paddle is usually my baking accessory of choice anyway, there are times I wish I could use the scraper with my whisk for better results—of course though, that's not really possible.
Worth the price? That's purely dependent on your baking needs. For me, it falls into the cool and fun (but by no means necessary) category.