Some wines (usually white) are left in contact with their lees to increase the complexity and enhance the structure of the finished wine. By leaving the juice to remain on top of the lees (and/or occasional stirring) after fermentation, all the dead yeast and skins, etc., can provide additional flavors, body, and richness. (Wine weekly)

We recommend racking and aerating the wine, with temporary removal of the lees. This practice has the double advantage of eliminating unpleasant odours and making it possible to continue ageing on the lees. The lees are kept separately in barrel and stirred frequently, then put back into the wine (VITIS-VEA)

During wine aging on lees, some membrane lipids of yeast lees, in contact with dissolved oxygen at low concentration, may undergo mild oxidation explaining the capacity of yeast lees to consume oxygen. (CAT.INIST)