Until a certain amount of revs the car will be in vaccuum (the negative numbers) before it makes positive boost pressure, as max torque starts at 1800rpm then I assume the turbo starts to spool around then or just before so you will be on boost until you let go of the accelerator. Once you let go and you're cruising the car won't be producing any boost until you accelerate again, and that depends on how much you accelerate and how many rpm you are doing. So in essence you won't be constantly on boost, and you won't damage the turbo unless the car has been tuned to run more boost than the turbo can handle. Not sure what the efficiency range of our standard turbos are though.