Read in cider book -- NO head space and no buckets

I previously read a book on cider and one of the guy's primary principles was that you should have as little cross-sectional exposure to air inside the fermentation vessel as possible. To explain further, his advice was that you should only ferment in a carboy, and you should always keep the carboy filled up to the neck so that very little of the cider has contact with air.

I know that many here don't follow that procedure, as many use fermenting buckets or leave head space in a carboy. So, is this guy's principle really unimportant? Can someone shed some light/opinion on this topic?

Thanks!

During the initial stages of fermentation, when it is strongest and the yeasties are battling their hardest and producing tons of co2, it is perfectly fine to use a bucket. However, his sentiments are commonly passed around as advice on here. After primary you should always keep your ciders topped off as much as you can. This limits the likelihood of having oxygenation issues later on.