Before knowing about CG I used to apply two rounds of shampoo and finish with one round of conditioner every time I washed my hair. That's the way everybody uses it in my family. If you don't know about CG your main focus is to have your hair/scalp clean with shampoo (you don't know about sulfates being bad to your hair) and your ends detangled with a little conditioner (not too much because it will weigh down your hair, especially straight hair). Some people in my family have such fine and straight hair that they don't use conditioner at all - I've always used it as my hair is curly and dry but not as cowash or leave in, just after shampoo.
Also no men in my family use conditioner.
If most people are like my family, that would explain why shampoo bottles are so big. They use more shampoo than conditioner!