When you're building something new in a place where there are definitely no underground utilities, everything is much simpler. Simpler for the people doing the work, and simpler for the environment, since there is less risk of leaks, spills, and other issues. But if you need to dig something up in the middle of a city, for example among a large number of buildings, it's very important to make sure the new work doesn't lead to unpleasant consequences. Or very expensive consequences. There are companies like UCG HDD that work with technologies that allow them to determine where different utilities are located so they can be properly avoided. Maybe some people still rely on regular maps and plans, but I'm not sure those always contain up-to-date information.