IMO, and from working on turbos as a carrier, a Turbo Timer is a great thing to have. True, not everyone needs one if you have time, but if your heading over to the store, having fun on the way, the last thing you want to do is wait in your car for the thing to properly cool down. It doesnt matter how turbos are cooled. Oil, Coolant or both. Its always good to let the oil and coolant circulate after driving hard. If you have just been cruising not really boosting, then its not necessary. If you have been hitting it hard and then come to your destination quickly, you really dont want to turn your engine off. All oils can cake if they get hot enough, no matter the grade, weight, etc. Ive cracked open many coolant lines to find burnt build up reducing efficiant cooling to the turbo, which can and will lead to a rebuild long before its due.
Is a Turbo Timer Necessary? Not if you want to take the time to bring your engine to idle temps.
Turbo Timers also provide other advantages which is nice. My HKS has a Battery volt meter, RPM reader, Warnings which act as shift lights as well, its a good investment in my book, but too each his own.
Sorry dude... lol you're wrong. (I'd google it and find the tons of articles that prove it but... no time for that) But that's ok... better to be safe than sorry I guess. I mean.. hell, I've got one!