Can I flatten nails from house siding?
Both comments above by Harper and bib are good reasons to start, but the biggest issue I see with bending over the nails is what the nails will do as they are being bent. The shank of the nails are substantial enough as when being bent over, the nail will shift to the side before it bends. The wood that the nail is in is typically not strong enough to keep the nail perpendicular as it was originally driven, especially if it is 1/2" plywood. This increases the chance of the large head on the exterior side to crack what it is driven through or crack the material over it, if that is the case. If it is wood siding, it could crack that, if it is cement board siding, it will do bad there too, especially if it is a nail on a corner.