Decisions made on legibility, readability, aesthetic appropriateness and even personal favourites inform a designer’s choice.
Choosing one on its life-saving ability, however, doesn’t rank high on the meter, but:
Bad typefaces can kill.
A bold claim - but when it comes to health education and user instructions font choice is especially important, as researchers Song1 and Manly et al2 found. Typefaces that are hard to read stop a user engaging with the information. When that is the difference between someone taking their full course of diabetic medicine correctly and not, it can have huge implications.