Usman Sabuwala when you get hired, you might get to work on multiple existing projects, some older than others and you can't just simply upgrade your version because some things may break due to compatibility issues or something. That's why you need tools to control the version you are in, so that you can work on different projects, that have been started in different dates but still need maintenance/features. Probably there's more reasons, I'm just starting out and this is my main one.