[Great68]

It depends on the nature of the easement. Most commonly it's to allow access/throroughfare for infrastructure. In that house's case it was so the neighbor's drains could get to the city infrastructure, and in that case yes it would prevent being able to build anything on that chunk of land. (well you could build on it, but the neighbour would have the right to demolish whatever you built to be able to service his drain system).