No particular reason; I have a shift+[ shortcut in Drafts that makes the switch between recent files almost instant. I’ve done both and ended up sticking to a separate file with questions.
Follow up: How do you quickly import the questions that you write in the plain text file into Anki? And how do you organize information into different decks?
I have one deck only because of mixed practice (ref: https://youtu.be/cwaWHeyK_aM). As for import, it sucks. Currently I just copy & paste them on my iPad.
