KrazyKraut

no moses, i'm not kidding, tell the others.

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There are two basic kinds of turbo cooling.
1. Oil. If you are running hard and shut down, the turbo is super hot and the oil is just sitting there getting cooked. This is especially bad with regular oil. The lighter fractions of the oil bake off leaving the 'coke' behind.
this is basically crud that now blocks the flow of cooling oil next time you run the car. Over time its like a heart attack. Not enough oil gets through and the turbo eventually has a meltdown (warped shaft, and thus wasted turbo)
This type gave rise to the market for turbo timers and Synthetic oil (which is much more resistant to coking). These helped the then current designs, but was only a band-aid. The solution follows...

2. Water. Watercooled turbos don't have the above problems and the metals used are designed for normal use. Yes, it might be better to let it idle for a minute or too to cool slower, but its not really needed. I usually just go easy on the gas the last few minutes of driving before shutdown.

ps, hard driving has nothing to do with speed. Its how much pedal you are using compared to how fast you are going. i.e. if you floor it but you are going slow, its a lot of stress. If you are going 90 with light throttle, its not much load.