The point is that you don't have to be around while it is cooking. Slow cookers can be used for a number of different recipes.
You can make stock in it. Stews and bean dishes are great in a slow cooker. Any tough cut of beef or pork can be put in a slow cooker. Then you can go to work or spend the day doing other things and when you come back hours later, dinner is ready.
Some people use them for various fruit butters; because they cook at low temperatures for a long time, there is no concern over scorching or burning.
Another benefit is that it does not produce a lot of extra heat like an oven. So a dish can be left to cook all day without using a lot of energy or heating the kitchen.
As phatch pointed out, read the manual. The cooker is not for boiling and the manual should have a some recipes you can try.