How significant is PhD's impact on someone's career? What I heard its mostly for academic and research purposes, Would you consider studying PhD?

It depends on your career aspirations. It may be necessary for some job requirements. Business development not required in my experience.

I hate school, so I'd never consider it; I don't care what job requires it.

I'm never going back, man.....

It has very little impact in the real world unless you want a research job or to lecture. Might impress the odd older manager but the status it once conferred (maybe 30 or 40 years ago) no longer exists.

Kind of rightly really. A lot of PhD problems are pretty specific. And it doesn't make you a good engineer.

Not at all if you are not willing to get old by teaching in uni. But that applies only at my country