Site safety measures and technical solutions (i.e. scaffolding, safety nets, and scissor-lifts) take priority over personal safety equipment (harnesses, climbing ropes, anchors).
The use of personal safety equipment should be implemented wherever the entire site cannot be secured, or where working on a platform would be more dangerous than roping up. The argument that “scaffolding is expensive” does not justify not building one.
Rescue should always be possible with the equipment on site.