Acts as a magnesium-dependent phosphatidate phosphatase enzyme which catalyzes the conversion of phosphatidic acid to diacylglycerol during triglyceride, phosphatidylcholine and phosphatidylethanolamine biosynthesis and therefore controls the metabolism of fatty acids at different levels (PubMed:20231281, PubMed:23426360, PubMed:29765047, PubMed:31695197). Is involved in adipocyte differentiation (By similarity). Recruited at the mitochondrion outer membrane and is involved in mitochondrial fission by converting phosphatidic acid to diacylglycerol (By similarity). Acts also as nuclear transcriptional coactivator for PPARGC1A/PPARA regulatory pathway to modulate lipid metabolism gene expression (By similarity). {ECO:0000250|UniProtKB:Q91ZP3, ECO:0000269|PubMed:20231281, ECO:0000269|PubMed:23426360, ECO:0000269|PubMed:29765047, ECO:0000269|PubMed:31695197}. This is the function of LPIN1 (lipin 1, Ensembl gene identifier ENSG00000134324).