In Dawn of Empires on Roblox, development appears to mainly boost a city’s economy and growth : it increases tax collection, manpower production, resource income, and population growth, while also raising the city’s tier each time it finishes developing.

What it does

  • Improves city income and manpower.
  • Raises the city’s tier with each completed development.
  • Makes the city stronger overall, especially for long-term economy and military support.

Important downside

  • Developing a city takes time, and while it’s being developed, recruitment is delayed there, which can leave it more exposed to attack.

Simple way to think about it

If you want a city to become more productive and useful over time, you develop it. If the city is near the front line, it can be risky to invest in development right away because it becomes temporarily less useful for military production.

The game also looks like it has a “Taxation & Development” focus in community guides, which matches that economy-growth role.

TL;DR: development = better economy, more manpower, higher city tier, but slower recruitment while it’s happening.