What Shimano have to say about the chainrings on my bike (From bike.shimano.com; I’ve reproduced it here becuase I rather suspect they’ll move the page and the image one of these days, and I want persistent reference.):
Reduced slippage under load: Shift pins and ramps are placed in the chainrings to ensure that shifts are executed at specific points in the pedal stroke — when riders are applying the least power to the pedals — reducing the chance of the chain slipping, and ensuring proper function.
Shimano patented performance: Shimano pins feature proprietary design and are placed at a specific angle that allows them to effectively pick up the chain even as they wear — making for sustained, predictable performance, even as you rack up the miles.
Advanced Tooth Profile: Look closely — the teeth on a Shimano chainring vary considerably in shape depending on their position. The tooth shapes are optimized to further enhance and facilitate shifting in perfect conjunction with the pins and in harmony with the rider’s natural fluctuations in power output.