It's more to keep the engine running - the turbo will continue to spin of its own accord as soon as the engine is switched off and that is the problem.
A turbo timer keeps the engine running which lets the oil circulate otherwise with the heat in the turbo you will fry off the oil and you will seriously damage your turbo.
When the engine is off the oil is no longer being pumped round and with a turbo spining at 100,000's of RPM it will quickly degrade its own lubrication. This can also cause sludge build up. So its always best to let a turbo engine cool down a bit before you turn it off especially if you've been doing some high rev driving
