Icing has several benefits. It helps some people with pain. It also helps reduce swelling. Those are the reasons I use it. Heat can also be of benefit, but not always is the case. Every part of RICE is equally important. You don't have to do them all at the same time. But try to do them as often as possible. Life can get busy, but it shouldn't be so busy that you can't heal yourself. In regards to icing after surgery, it should be ok to use. Though check with your doctor to make sure. Also, ice can damage your skin if left on to long. Depending on the type of ice pack you're using, it could be 15 minutes to a half an hour or so. Just remember one key thing, take care of that knee. Nothing will ever replace it.