My factory boost controller has been modified to give up to 13-14 psi, I have a switch turning it on and off. Boost gauge doesn't like regular changes though.
Clutch slippage, low boost till fixed. (done)
Coilpacks going, low boost till fixed. (done)
L plater girlfriend driving, low boost.
Car feels different, still nice to drive just a bit slower, I actually preferred it for a while.
Traction on nankangs is poor, esp in the wet, low boost helps as the stock turbo is insanely responsive and quickly goes from 7-14psi, wheelspin. Also with stock turbo there really isn't much difference between 7 and 14psi in terms of right foot position, just in power. The boost curve is weird because I don't have an electronic boost controller. 7 psi by 3000rpm, 14psi by 3100rpm.
Not sure why you'd do it with an actual boost controller. I did it to help the turbo, and the above reasons.
It's not going slower I was after, it was less boost, less engine stress. I preferred the switch.