This area is being discussed where I have just starting working: as breathable membrane (such as vent 3) has been used as building paper (such as tyvek house wrap).
As much as I can see BM should be used only on roofing and should not be used against a solid boarding such as Ply or OSB, where as BP (which is also breathable) can be used against a solid boarding on walls and roofing externally (with proper ventilation in the next external layer).
A new built single story timber frame extension which is being retrospectively treated with catastrophic damp problems (last builder to look at job suggested to knock down, an option not entirely ruled out) has, among other problems, vent 3 (same stuff, different name) on the timber frame with vented cladding on top. As the timber frame is at ground level (with dpc) we have noticed that the BM sucks up water and brings in into the timber frame. This is also being caused by bad workmanship, but I have a strong suspicion that we can see that vent 3 will draw and hold on to ground water though capillary action, where Tyvek is less sponge-like.
Hence vent 3 should not be used esp. on anything below 1m up from finished ground level. Also it should be 'hung' between beams, or with support with an insulation such as Celletex. It has insulating property's to help reduce condensation under slate, as well as being a barrier to reduce weather problems.
To save £50 buying a smaller roll of material (with the same meterage cost) against possible £1,000's costs altering work, is not worth it.