Additional to the above comments about the compass being swung with the pitot heat on etc.. just consider this:
When during an otherwise uneventful trip your flight visibility starts to diminish, your navigation workload starts increasing exponentially and your spare mental capacity is rapidly disappearing to zero.
Will you have the presence of mind to check the OAT, then correctly evaluate the prevailing conditions and respond by turning the Pitot heat on?
Will you notice the insidious errors creeping into your pitot/static instruments in sufficient time?
Does the reduced electrical load and extended life of the pitot heaters in any way justify not using pitot heat?
Better to turn the sucker on whilst lining up and you still have two spare brain cells to rub together.