That's an excellent observation! You've spotted a key detail in good public design. The short answer is yes, that slight curve is absolutely intentional and does make a significant difference in comfort, especially for longer sits. Let's break down why.
Unlike a flat, straight backrest, a gently curved bench conforms to the natural "S" shape of the human spine. This provides crucial lumbar (lower back) support, reducing the muscle strain required to stay upright. A flat bench forces your back into an unnatural, straight position, leading to fatigue and discomfort much faster.
The curve also creates a subtle sense of enclosure and psychological comfort. It offers a gentle, supportive "hug" that makes the seat feel more secure and inviting than a stark, flat plane. This design encourages people to linger, which is the ultimate goal for parks, plazas, and communal spaces.
Furthermore, the curve is often part of a holistic ergonomic design. It's frequently paired with a slight downward tilt to the seat itself, preventing you from sliding forward, and a carefully calculated seat height. This trio of features—curved back, tilted seat, and proper height—works together to distribute body weight more evenly, reducing pressure points on the thighs and backside.
So, while a simple flat bench serves a basic function, that thoughtfully designed curve transforms it from a mere place to perch into a comfortable place to rest, converse, and enjoy your surroundings. It’s a small detail with a big impact on how we experience public spaces.