The simple fact that caramelized onions can change the taste of any food you cook is a good enough reason to use them in as much as possible. My first experience with them on the BGE was making baked beans. Now, they are used on my pizzas, pasta dishes, soups, and any other way I can think of using them.
It takes about 25 mins. to get them cooked, but at the same time it depends on how you slice the onion …. chopped seem to cook a little faster than sliced. I guess it just depends on preference.