The warm air does help the engine warm up quicker in the winter - translates to heat inside the cabin sooner - BUT it also reduces emissions, and as such, it is an item that is inspected in some states during emissions inspections. Easy and cheap to replace the thermostatic element, but as long as you secure the flapper shut if removed, you shouldn't have any problems. Note that on the later engines (1990-) there is no preheat thermostat flapper or preheat hose from the manifold.