[richardjdare]

For me, the appeal is not so much that Emacs is customizable, but that it's basically a live coding environment for working with text, seamlessly integrated with all the usual functionality of a text editor.

I often write short programs interactively to manipulate the text I am working on, and have a whole bunch of Elisp code for common things that come up at work. For example, transforming a pasted ad-hoc spreadsheet column into sql insert statements (because nobody wants to pay to add that functionality to the software, and they email me instead). I used to have a bunch of code for generating Java boilerplate, and even entire classes but the situation has improved in recent years...

Sure I could write scripts or conventional programs to do these jobs, I just prefer the interactivity and fluidity of Lisp environments. Also, being an Emacs user means I can write Lisp at work and get away with it.

Having said all that, I tend to primarily use a dedicated IDE, with a general purpose text editor in the background. I will use Emacs alone when I am writing plain text, Common Lisp, or simple stuff that doesn't require a load of configuration or a complex toolchain. I want the IDE to take care of that for me.