Bottom line, your tip helps your driver keep their head (barely) above water. If you tip at a sit-down restaurant*, tip your delivery driver.
*if you're in the US and don't tip at sit-down restaurants, I don't want to know you.**
**this is not the place to debate tipping in the face of poor service. I still don't want to know you. Leave a note with the tip or talk to a manager about why you're unhappy.