When I was younger and walked all the time I used to carry 6, then as I got older and rode a cart most of the time it because closer to 20-30 as I never emptied the bag of scuffed balls. Never really had a reason since I never carried the bag. At the end of the year I'd clean it out and start over again the next year. Now, I try to mix it up ride, walk, and push cart so I'm trying to keep it around 6, unless I'm playing a course with a lot of hazards then I might throw in an extra sleeve and if I have to play a ball with scuff marks or one that was cut by my wedges so be it. It is better than killing my back with a few dozen balls.