Small GTP-binding protein that plays a central role in regulated exocytosis and secretion. Controls the recruitment, tethering and docking of secretory vesicles to the plasma membrane. Upon stimulation, switches to its active GTP-bound form, cycles to vesicles and recruits effectors such as RIMS1, RIMS2, Rabphilin-3A/RPH3A, RPH3AL or SYTL4 to help the docking of vesicules onto the plasma membrane. Upon GTP hydrolysis by GTPase-activating protein, dissociates from the vesicle membrane allowing the exocytosis to proceed. Stimulates insulin secretion through interaction with RIMS2 or RPH3AL effectors in pancreatic beta cells. Regulates calcium-dependent lysosome exocytosis and plasma membrane repair (PMR) via the interaction with 2 effectors, SYTL4 and myosin-9/MYH9. Acts as a positive regulator of acrosome content secretion in sperm cells by interacting with RIMS1. Plays also a role in the regulation of dopamine release by interacting with synaptotagmin I/SYT.