That's an excellent and insightful question. To answer directly: yes, in many cases, the specific design and placement of armrests on public park benches are intentionally used as a deterrent to prevent people from lying down and sleeping on them. This practice falls under the broader term "hostile architecture" or "defensive design.
While armrests can provide legitimate comfort and assistance for the elderly or those with mobility issues, their primary function in many public spaces has shifted. A single, continuous bench seat could easily accommodate someone resting flat. However, by installing fixed armrests at regular intervals—often in the middle of a long bench—the seating surface is divided into individual, chair-like segments. This physically prevents a person from stretching out, making it impossible to lie down comfortably.
Proponents of this design argue it maintains benches for their intended purpose: sitting. They claim it discourages long-term occupation, reduces perceived loitering, and can help with maintenance and cleanliness. However, critics strongly oppose this approach, viewing it as a form of social control that unfairly targets homeless populations. Instead of addressing the root causes of homelessness, such designs effectively make poverty less visible by pushing vulnerable individuals out of public spaces. It raises ethical questions about who public spaces are for and how cities choose to manage social issues.
So, while not every bench with armrests is designed with this intent, the widespread use of segmented benches is a clear architectural strategy. It highlights a conflict between public order management and social equity, turning an ordinary piece of street furniture into a symbol of a much larger urban and societal debate.