Fairly sure I read somewhere it causes the metal to prematurely crack due to heat it wasn't designed for. Usual suspects might confirm?
Wrap the header near the hot air pipes coming from the heater boxes to make them last a bit longer if you have a 4 into 1 . But generally no it falls off as it goes brittle. Thats what happened to the fibreglass wrap I tried. Just turned into nasty fluff.
I once wrapped my 4 into 1 header and exchangers, worst thing I ever did, engine temp went through the roof, some did say to me better of not wrapping as you need the air flow across the metal to dissipate the heat, makes sense I suppose, Have seen others wrapped and they say have been fine, make your own mind up I suppose.