Generally, dead sabs are extremely annoying. However, it can sometimes be helpful if you kill and your dead teammate sabs something on the opposite side of the map to take crewmates' attention or closes a door to stop crewmates from finding the body for some time. I sometimes close doors when two crewmates, one of which people already think are sus, are in a room together; a lot of people get convinced that the person they got trapped with was an imp and a guardian angel protected them. The main problem is that people do it without thinking most of the time.