What does a turbo timer do?? Also, how necessary is it to get one??

for the 2002 WRX it's more simply known as "GGG" or gas guzzling gadget. Basically it just wastes fuel while idling. You have the option to stay in the car or not though while it is operating.

Unfortunately it has no performance benefit either!!

It does have a nice side benefit for your peace of mind though...
Kind of a psychological mod?