Having their own bedroom will help children in life in ways we often do not imagine, as well as will make them more responsible and mature.
Allowing children to decorate their room as they wish gives them the freedom to express themselves in their own space. At the same time, as they get older and privacy becomes more important, their room will enable them to keep their things safe and to have a place where they can isolate safely and quietly when they want to, especially if there are other younger siblings.
Finally, having their own room allows them to invite friends while giving them a sense of pride and responsibility as they will want to keep it tidy.