The purpose of a blow-off valve is to release built up pressure in the compressor housing into the atmosphere, significantly reducing the likelihood of backspin
the turbo stays spooled up, there is no compressor slow down due to stacking.
and the turbo lives longer due to boost not stacking up on the compressor blade.

Stacking is when the pressure in the intercooler hose's is greater than the turbo output- that's the noise you hear when you change gear with an element air filter, and it's very bad for the turbocharger.

With a high boost engine stacking is even worse!