RAB, Thanks for the advice - its something that was covered in our beginners course and discussed along the lines of something we should do rather than could do, I cant remember our tutor's stance but I know we came away thinking that as newbies who just want to do the best for the bees we should do it.
Its easy to see how things like this become the norm and you feel you should do it "just in case".
So just to check I've got it right - I should only consider feeding winter fondant if the hive starts to heft too light.
The problem I anticipate is as a newbie how do I know what too light is? Seems I'm off to look for a scale hook thingy so I can actually check it rather than guess this year - then when I get more hives/experience I'll be able to judge it by hefting.