In a response to the question “Why emacs?” on news:comp.emacs, Brian wrote:

I first ran into an implementation of Emacs on a MULTICS system in 1982. Initially, I was intimidated by it because I did not really understand how to use it. Any time I run into that kind of scenario, I an intrigued by it.

I joined Digital Equipment Corporation (DEC) in 1985 and again I was presented with the opportunity to learn more about Emacs. This time, I found more than one implementation of Emacs. I found a VAX/VMS implementation of Emacs that was based on a variant of the Carnegie Mellon University version of Emacs that later became known as Gosling Emacs.

Not too long after that, I was introduced to an Emacs variant called Elle that ran on VAX ULTRIX systems. Soon after that, I found GNU Emacs.

It was when I started using GNU Emacs that I found online resources where I could learn more.

I used it at first because it was there and because I was inquisitive. I found that I could emulate other editors with Emacs, which was a plus, because I could use it before I really understood it well. I found Vi emulations available and also emulations of two editors that were common at DEC in those days: EDT and WPS. I started to use those emulations, and soon Emacs became my every day editor. Meanwhile, I endeavored to learn how to use it correctly and also how to define my own key bindings. Once I did that, I was home free, this became my every day editor. I could run it on proprietary systems, such as VMS and UNIX systems, and later, I found I could run it on other systems, too.

These days, getting started with Emacs is a lot easier; documentation is better, and so are the tools that are available. Emacs is worthwhile because it can handle just about any development need I have, including reading and writing news. I’m using Gnus, a mail and news reader that’s integrated into Emacs to respond to your inquiry.

There is plenty of information out there about Emacs. If you want descriptive details, look for that information online, Google can find it for you and others have already suggested some places where you can find it. I assumed that you were looking for opinions, background, and reasons why people chose to use Emacs. Personally, I chose it at first because it was there, I continued to use it because it could handle any editing task I could throw at it.