Why management?
According to Wikipedia, Management (or managing) is the administration of organizations. and A supervisor is first and foremost an overseer whose main responsibility is to ensure that a group of subordinates get out the assigned amount of production, when they are supposed to do it and within acceptable levels of quality, costs and safety. While management/supervision in academia is sort of a dirty word, these should not be intrinsically bad things: a group leader wants their group to function as best as possible. It just has to be done appropriate to the situation.
Lack of good supervision can cause plenty of problems, such as inefficient work, lack of diversity in academia, and major mental health problems.
Get the most out of your group
You want to succeed, that means your group needs to succeed
People can and will struggle without you
This isn’t about doing things for people, but making sure they can do their best and don’t struggle with solved problems.
Societal impact
Are you just trying to race for promotions or do you also want to improve society?
Academia gets funding because it should help society. This doesn’t just mean research output, but also trained and competent researchers ready to contribute in other ways.
Help people
Good management is good support
Good support lets people advance the fastest
Do we even need to discuss if you should care about your employees/students?
Improve the quality of life for your group
People struggling aren’t happy
People not happy can’t be as productive
Avoid “rich get richer”
Academia is know for its many diversity problems
If you let people figure it out, the ones with their own support network will tend to succeed more.
Or worse, if you aren’t thoughtful about your supervising, you end up supporting your favorite workers the most.
This probably isn’t what you want. But it might be what you get if you don’t pay attention.