The function of the autosuture is to seal closed and promote the healing of wounds from surgery or deep trauma by stimulating the patient's own anabolism. It is used where the dermal regenerator is inadequate.
Doctor Phlox used an autosuture during his operation on Porthos in 2152. It was used to secure the placement of the pituitary gland he transplanted from a Calrissian chameleon. (ENT: "A Night in Sickbay") Shortly thereafter, he traded his autosuture, among other things, for deuterium. (ENT: "Marauders")
Dr. Julian Bashir used an autosuture to repair an injury to Martok's shoulder during a training exercise with Worf. While the repair was general, had the wound been three centimeters to the right, Martok's brachial artery would have been severed, causing much greater damage than an autosuture could repair. (DS9: "Soldiers of the Empire")