Some people do this simply because they do not want to always show up at work 20 minutes early just in case they have a mechanical but also do not want to have to show up late because of a simple problem. I know one guy who spent a lot of time riding in some pretty exposed areas that are known for storms coming in incredibly quick so he would carry a pump and a co2, the co2 was simply in case he got caught out in a lightning storm and flatted.