It depends on what you are cooking. If it's a roast or chicken and potatoes, you can put a few potatoes in, put the roast or chicken on top, sprinkle some seasoning, turn it on and leave.

If it's a stew or something like that, of course there is going to be some prep work, but you can do that the night before. I do all the chopping and the rest the night before, put it in the fridge overnight, and in the morning on the way out the door put the liner in the crockpot, set the timer and it's done when I get home.

There is little advantage to using the slow cooker over a pot on low on the stove all day, or if your oven has it, the slow cooking function of your oven. Again it depends on what you are cooking, but people cooked stuff long and slow ages before a crockpot came around.

The real advantage is you don't need to be there or watching it, you can leave it on the counter all day, which most people would not feel comfortable doing with a pot on the stove.

Granted, there are people who don't like leaving a crock pot on when they are not home too, but for the most part, that's where it has the advantage.