Binds to lipid droplets and regulates their enlargement, thereby restricting lipolysis and favoring storage. At focal contact sites between lipid droplets, promotes directional net neutral lipid transfer from the smaller to larger lipid droplets. The transfer direction may be driven by the internal pressure difference between the contacting lipid droplet pair. Its role in neutral lipid transfer and lipid droplet enlargement is activated by the interaction with PLIN1. May act as a CEBPB coactivator in the white adipose tissue to control the expression of a subset of CEBPB downstream target genes, including SOCS1, SOCS3, TGFB1, TGFBR1, ID2 and XDH. When overexpressed in preadipocytes, induces apoptosis or increases cell susceptibility to apoptosis induced by serum deprivation or TGFB treatment. The physiological significance of its role in apoptosis is unclear (By similarity). May play a role in the modulation of the response to osmotic stress by preventing NFAT5 to translocate into the nucleus and activate its target genes expression. a triacyl-sn-glycerol(in) = a triacyl-sn-glycerol(out) Homodimer (By similarity). Interacts with CEBPB (By similarity). Interacts with CIDEA (By similarity). Interacts with PLIN1 (By similarity). Interacts with NFAT5; this interaction is direct and retains NFAT5 in the cytoplasm. Diffuses quickly on lipid droplet surface, but becomes trapped and clustered at lipid droplet contact sites, thereby enabling its rapid enrichment at lipid droplet contact sites. Down-regulated upon hypertonic conditions. The CIDE-N domain is involved in homodimerization which is crucial for its function in promoting lipid exchange and transfer. Ubiquitinated and targeted to proteasomal degradation, resulting in a short half-life (about 15 minutes in 3T3-L1 cells). Protein stability depends on triaclyglycerol synthesis, fatty acid availability and lipid droplet formation (By similarity).