The netting may be loosely draped or cinched up tight. It depends on the building. The effect of the former is not unlike a veil, while the latter suggests something more like a corset. In either case, the purpose is the same: to prevent problems caused by falling debris.
With buildings still in use, exterior cladding sometimes ages poorly or gets damaged by an earthquake or a typhoon. The rest of the building is effectively fine, though, so it gets the tightly wrapped net, the borders contoured around doors and any windows necessary for emergency egress.
With a derelict house, however, the problem is just that the entire structure is falling apart, and becomes apt to shed parts of itself onto the sidewalk or street without warning, especially if the wind kicks up. And so, the coarse net is draped over them in great green swaths.
There are several such abandoned houses in my neighborhood. One stands on an overgrown, jungle-like lot with a corroded, corrugated metal fence around most of it. The siding is falling off, many of the windows are broken, the roofing is coming off in sections, and the exterior steel staircase is all but entirely rusted through.
Around the building, like a supplemental set of bones, stands a framework of steel scaffolding. Wrapped around all of it is the net.
It reminds me of a broken-legged racehorse with a tarpaulin drawn over it before the injection, or a shroud wrapped around the recently deceased. The damage is too severe and cannot, will not be healed.