The purpose of the preheat hose is to slightly reduce emissions during the brief warmup period until the mixture control goes into closed loop operation. It has no effect on starting, performance, time to warm up or "defrosting" the manifold. In other words it's to keep the environmentalist global warming wackoes a bit quieter so it's probably worth having it on there.
The only downside is if the thermostat sticks you can fry the AMM.