Product Management - How Do You Seek to Split Up Roles?

If you're a startup and you're listening to this, you're probably lucky to have a product manager. But let's say it's a more mid-sized to larger-sized company. How do you expect to draw those lines? When do you know to split up the roles in those sorts of things? You can start to think about why separation is an important thing. There's speed. There's efficiencies. Some cases could be less dependencies, but there's still a pace car that is determining how fast things can get done and out the door.