May play a role in vesicle-mediated protein trafficking to lysosomal compartments and in membrane docking/fusion reactions of late endosomes/lysosomes. Required for proper trafficking and targeting of the collagen-modifying enzyme lysyl hydroxylase 3 (LH3) to intracellular collagen (PubMed:28017832). Mediates phagolysosomal fusion in macrophages (PubMed:18474358). Proposed to be involved in endosomal maturation implicating VIPAS39. In epithelial cells, the VPS33B:VIPAS39 complex may play a role in the apical recycling pathway and in the maintenance of the apical-basolateral polarity (PubMed:20190753). Seems to be involved in the sorting of specific cargos from the trans-Golgi network to alpha-granule-destined multivesicular bodies (MVBs) promoting MVBs maturation in megakaryocytes (By similarity). {ECO:0000250|UniProtKB:P59016, ECO:0000269|PubMed:18474358, ECO:0000269|PubMed:28017832, ECO:0000305|PubMed:20190753, ECO:0000305|PubMed:23918659}. This is the function of VPS33B (VPS33B late endosome and lysosome associated, ENSG00000184056).