That's an interesting question about a common urban feature. From my observation, the main pro is that it provides a designated spot for smokers to dispose of their cigarette butts. This can significantly reduce litter on sidewalks and around the bin itself, keeping the area cleaner and reducing fire risks from hot embers. It's a simple courtesy that acknowledges a public behavior and tries to manage its waste.
On the flip side, there are some clear cons. First, these ashtrays often need frequent and careful cleaning; if neglected, they become overflowing and unsightly, defeating their purpose. They can also normalize smoking in public spaces, which might conflict with health promotion goals. Additionally, the concentrated butts can sometimes smell, and if the ashtray isn't designed well, wind can still scatter the waste. Ultimately, it's a practical solution to a specific litter problem, but it's not a perfect one and requires consistent maintenance to be effective.