I think it is placing unnecessary stress on the manifold. It's good for NA cars, where they are wanting to increase gas speeds to take advantage of scavenging from large duration camms. You don't have that kind of duration on a turbo car, and with big boost, you are unlikely to be able to fill the cylinders anymore.

THe exhaust gas temps on a turbo car are astronomical, by keeping this heat in, you are increasing the risk of both manifold and valve failure. Sprint car yes, road car no. I wrap the areas of the exhaust which run close to things like pipes or cables, to keep the heat away from them. Wrapping the downpipe works too. Wrapping anyfurther than half way is a waste of money - the gases will have cooled dramatically by then.