At certain times, space can be limited in the vat room for several reasons: high yields, purchasing of new plots, racking has begun and certain vats are unavailable, and /or lack of a wide enough range of containers to choose from, etc.
When these situations arise, the winemaker may find themselves with a partially filled vat. This can be highly detrimental to the quality of the must and the future wine. Excessive contact with oxygen can cause undesirable oxidation. It is imperative to protect the partially filled vat by filling the headspace with an inert gas before and after fermentation.