Project management is important for projects you do alone. Some people maybe think it's just for team projects. But by yourself it's still useful to have some idea of what tasks go into a project, estimate how long they'll take, estimate resource costs per task (e.g. how much money you'll have to spend), etc. Then you can look at your schedule and budget and see how long it'll take to get the project finished. And then you can consider: is it worth it compared to alternative projects?
A project merely means doing multiple activities/tasks over time which are meant to work together to achieve one or more goals. That's something people do alone or in informal, non-business settings. And it's something that can go wrong. There are plenty of ways to be disorganized and screw it up. So people have developed ways to better plan, evaluate and organize projects. But most people aren't taught them in school and don't go find out for themselves either, which makes their projects unnecessarily difficult and risky.
(In my opinion, the best project management author is Eliyahu Goldratt.)