To get the haircut that you want, consultation is key, which is why I put so much value on it.
As opposed to asking 'how short?', typical questions I would ask might be...
"Do you like your hair better the days its cut, or the week after?"
"What annoys you about your hair?"
"Do you want your hair to look like you care it looks good or that it accidentally looks good?"
"Do you want it to move during the day or stay put?"
"How soon do you want to come back?"
"Different for YOU, or different for the world?"
"Would you rather make this part look good when it sticks up or spend as few minutes drying to make it sit down?"
"What did or didn't work last time I cut your hair?"