I normally wash mine everyday just because I have oily hair and it stinks if I don't lol If my hair wasn't oily I wouldn't wash it everyday. I have been told at the salon that it isn't good to wash your hair everyday because it can dry it out therefore it could become weak and spilt causing damage. You can always skip a day and see how it goes for you.
It is not good to wash your hair everyday unless you have oily scalp. This is because frequent washing can cause the scalp to dry and you will dry out the natural oils for your hair making it friz, dry, brittle and unhealthy. It is recommended that one should wash the hair at least three times a week.
It depends on what kind of hair you have. Do you have baby fine hair, or thick hair? Is your scalp oily , dry or normal? Do you have straight hair or curly? if you have baby fine hair then you shouldn't wash it every day unless you filthy it every day. Wash it every other day and use a spray in conditioner with a volume or fine hair shampoo so that you even things out. Curly hair doesn't become oily as fast as straight hair does.
I have thick straight hair with hair strands that are twice as thick as normal hairs so my hair doesn't damage as easily as someone with fine hair. I wash it every day despite the length because it easily gets oily. I just use a volume or hair repair mixed with deep cleansing shampoo and leave in spray conditioner.
Everyone's hair is different and you need to find what works for your hair. washing your hair once a week is taking it overboard though, no one needs to be that filthy.