Exercise is important for keeping our minds and bodies healthy. it can help to reduce the risk of a range of diseases such as coronary heart disease, a range of cancers, stroke and type 2 diabetes as well as reducing symptoms of depression and anxiety.
Exercise alone will not help you lose weight. You can only lose weight from changing your diet. I've been fooled by this myth for a long time and am sad to find out it isn't true, but we can't ignore the research.
For more info see this article from the guardian.