Having studied and applied management theories myself I can tell you that bits and pieces of each work. I have not found one theory that I believe works in its entirety. Being acquainted with and understanding each theory helps you to recognize what action might work in a given situation in the workplace. Human nature being what it is, you will often find yourself flying by the seat of your pants and improvising.

I am of the opinion that people skills are far more valuable in management than most textbook theories. People want to be valued and respected. You give respeact, you get respect. A manager who is respected is well on their way to running the company.