Turbos, on any type of equipment (and my back ground is in diesel mechanics, where everything is turbo charged) must be cooled for longer life.

Cooling is accomplished by , collant and oil circulation.

When you work the turbo hard ie racing, heavy highway work, heavy loads, heavy throttle, etc, it is wise to not shut off the turbo , (engine) losing collant and oil circulation until you have reduced turbo temperature.
Reducing high throttle use, for a couple of minutes, when you come off the highway and use less throttle on secondary roads, this is normally enough to allow shut down.

The only time you should need to idle a turbo charged engine before shut down, is when you have extreme heat from a heavy work load application.

Hope this helps.

John
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90-740GL , 92-945Turbo