Short answer: no, urban planter boxes do not automatically need to be lined with landscape fabric. What they really need is a way to keep soil in, let excess water drain out freely, and prevent drainage holes from clogging. Landscape fabric can help with some of these jobs, but it is a filter layer, not a waterproof liner and not a substitute for proper drainage.
Landscape fabric is most useful at the bottom of a planter box, especially over large drainage holes or between potting soil and a coarse drainage layer such as gravel. In that position, it allows water to pass through while reducing the amount of fine soil that washes out. It can also help keep drainage holes from becoming blocked by silt or roots over time. This is particularly helpful in large urban planter boxes where soil movement can be hard to manage.
However, lining the entire inside of a planter box with landscape fabric is not always necessary. Plastic or metal boxes usually do not need side lining unless the drainage holes are oversized or the soil mix is very loose. Wooden boxes may benefit from a protective liner, but landscape fabric alone is not a waterproof barrier and will not prevent wood from staying damp. If wood protection is the goal, use an appropriate breathable or waterproof liner designed for planters, and always maintain drainage.
The main risk is blocking drainage or creating a waterlogged root zone. Never use landscape fabric as a replacement for drainage holes, and do not combine it with plastic sheeting that traps water. Even permeable fabric can become clogged with fine sediment over time, so check it occasionally and replace it if water no longer drains well. Wrap it loosely, secure it with gravel or clips, and make sure every drainage hole remains open.
In practice, use landscape fabric selectively. If your urban planter boxes have good drainage, a quality potting mix, and drainage holes that are not too large, you can often skip it. If soil is washing out or drainage holes are clogging, use landscape fabric as a simple filter layer at the bottom. The goal is not to seal the box, but to keep soil where it belongs while letting water move freely.