No more stressing over getting out of work in time. Sometimes I work late or end up with last-minute plans that keep me out later than planned. Even with the warm function on my slow cooker, I was never sure if I'd make it home in time to turn the slow cooker off, especially if it was a dish I was worried about overcooking like poultry.
A chance to check on the meal before serving. Every so often, I'd find out when I arrived home, moments before planning to serve a dish, that it wasn't quite cooked enough. A chuck roast would be a little tough and could have used another 30 minutes to an hour of cooking before becoming fork-tender. Being able to check on a dish in the morning before going to work gives me a heads up — I can plan for an hour of extra cooking time when I get home, for example.
Time for flavors to develop. When I make chili and braised beef ragu, an extra day spent in the fridge helps the flavors develop deeper than serving the dish immediately. This time gives a dish an extra level of flavor I couldn't get in the six to eight hours in the slow cooker alone.
Just warm and serve. Usually the meals I make in my slow cooker require skimming off excess fat, shredding meat, and other last steps before serving. If I can do these in the morning, then it's really just one step to warm and serve when I get home.
More time to make complicated recipes. I love slow cooker meals with a lot of prep. Searing proteins, cooking vegetables, and de-glazing pans make for more flavorful meals, and I like having extra time to complete these steps at night.