Most devs I've met use it, it's an excellent tool for getting rid of formatting or just having an instant window open where you can temporarily store some plaintext.
I just tested it now pasting some text from a website into Slack and it retained hyperlinks (I don't mean plaintext https:// ones, but <a href='..> ones) and all that junk. When you cleanse it through notepad you have a guarantee that none of that is left.