Sorry it's taken me ages to be back here!
You could ignore it, just means that if it gets really cold in winter it may get a little cranky, literally
They don't really need it, Transit's dont bother with them but they are not computer controlled so dont mind being cranked over with throttle applied if required. Common Rail's are different!!! They are really there to stop excessive cranking in ultra extreme cases, as they are like petrol Efi's and the enrichment is right up on startup. Mind you, from what i've heard it doesn't stop common rail Tranny's (injector earths out and goes on permanent, filling the cylinder with diesel
resulting in bent everything as it usually happens to them on m'way cruise, common apparently, but that's ford electrics for ya!
The circuit itself is usually (dont quote me as the last diesel i had was a 95 Escort) just a simple switch off when resistance reaches a certain value design, they take longer when it's colder as it takes longer to reach the temp and correspondingly the resistance.
It's only an issue if it refuses to start, but the remedy is usually simple, replace the faulty plugs!!