I don't own a turbo but I've been trying to learn as much as possible. From my researching, I've found that many people purchase turbo timers. I found this clipping at a really informative site:
The use of turbo timers to shut the engine off some preset time after the ignition key is removed was needed in the old days, when the turbocharger bearing housing was only cooled by the lubrication oil of a running engine passing by the turbine bearing. If the engine was shut of when the turbine was still hot, the old design saw excessive heat wick into the turbo bearing and seal area, causing failure and heavy oil consumption. The newer (for over 10 years now) style turbo housings are water cooled as well as oil cooled.

So why do so many people with new WRX's or new turbo's for that matter buy this thing?

BTW, here is that site:
A good informative site for WRX engines.

 

Looks like I missed copying more of the clipping:

The original EJ20 Subaru turbo motor took advantage of water cooled bearings from the start and have never had this problem due to a unique design feature.

The Subaru WRX engines have their water catch tank high on the engine above the turbocharger. When the engine is shut off the water continues to circulate via a physical property of water called a thermal siphon. Simply put, hot water rises up to the catch tank, being drawn from the relatively cool cylinder head water jacket up through the turbo housing. One still needs to take a cool down lap at the track and perhaps should not stop at the top of a mountain pass to enjoy the view if you have been on the boost all the way up, but for the other 99% of the time there is no need to let the engine idle for a minute before shutting off ignition. Even when the engine is off, the cooling water will circulate past the turbine bearing housing.

 

Turbo timers are generally for oil cooled turbos. Oil/coolant cooled turbos dont normally need a turbo timer.. which is why most factory turbo'd cars are also water/coolant cooled.

Turbo timers are also good for people that constantly beat on the turbo then immediately shut the engine off.

 

to cool down the oil, so the hot oil doesnt sit in the turbo and cook it dead.

its not a must have, u can physically sit there and be the turbo timer and let ur car cool off, just a gadget

 

Dude that is one of the nicest PGT's I have ever seen, I use to own one before my P5 and loved it, except the reliabitly (high mileage) Anyway that is exactly what I wanted to do with mine, keep it mostly stock except for the engine work and nice suspension and wheel package...

But what he said, you can sit in the car and let it idle before you shut it off. The turbo time will allow you to pull the key and leave the car, but will keep the engine running for X amount fo seconds before turning it off...

 

the compustar alarm/remote starter FM models have a turbo timer built into them as well

 

yes, that is the alarm ive been trying to acquire. very often, a turbo timer will interfere with how ur alarm is setup, becuz most alarms disarm upon shut off and u cannot arm it while it is still running. u can see how that will mess things up when u leave the timer running the car and walking off....u wont be able to arm it when it shuts off when ur gone....thats the problem i have with mind, so i wind up sitting there waiting for it anyways....unless im at home and can hear the car runs and activate the alarm when i hear it go off.

installshield....thanks for the compliment