For as far as I drive for work it is a must. I currently drive 65.7 miles one way to work. So that equals 131.4 miles a day.
Thankfully I have a job that allows me to work 7 days on 7 days off. When we first moved to our new house I was driving a 1992 Nissan pickup. It was getting 26 miles to the gallon, not bad but it was costing me almost $330 a month
Currently I have a 2007 Toyota Prius it averages 50 miles per gallon. Now with gas over $3 a gallon again it is only costing me $140 a month to go to work.
This is my best tank seance I bought my car a little over a year ago. 
53.1 miles per gallon and 358 miles total was on the tank, with a quarter tank left when I filled up.