Originally Posted by JCL

These oils have a pour point colder than -40 (C or F) so in that sense the heaters are not necessary, but for those that want to be kinder to the machinery, they aren't a bad idea. With the crankcase ventilation valve problems, the idea is that if the engine is already somewhat warm, it will warm up quicker once started, and that gives more time to boil off the condensation if you are doing short trips.

I like the oil pan heaters compared to coolant heaters, as they are entirely external, with no chance of leaks.