one being a straight line? ouch, that is kinda annoying to read and can be misunderstood easily.
seven having the '-' in it is kinda only useful if you write one as '1' not '|' - if someone has bad handwriting(ie me) it can me mistaken for 1.
i use dash in Z and z only in math - because of my crappy handwriting i sometimes can mistook it for 2.