Mostly it's the latter, out of a sense of duty. But there are other motives. Regular reviews give you some perspective that you otherwise wouldn't get. For exa

Mostly it's the latter, out of a sense of duty. But there are other motives. Regular reviews give you some perspective that you otherwise wouldn't get. For example, you see what mistakes others make and that can help you improve your own papers. Another motivation for me is sometimes that I don't want the paper to be reviewed by someone less qualified in my areas of specialization.