I normally wash my hair a couple of times a week and if I leave it longer it goes absolutely disgusting and my head just starts to itch like crazy so I can't stand it. I only ever use shampoo - no conditioner as it seems to make my hair go greasy faster (no, i don't put conditioner on my scalp) and doesn't really add to the shine anyway? Don't get the point of conditioner other than as a way to throw more money down the drain.
I know that shampooing your hair every single day can be damaging, much like washing too much because it doesn't give your body's natural oils enough time to sort themselves out. (Obviously that's a simplified version of what really happens.) Uhh I know that if you do have to wash your hair every day because it gets so greasy so fast you should empty half your shampoo into a second bottle, fill up both bottles to the top with water and then mix it together to dilute shampoo. Think I learned that from Bobbi Brown but it was never that important to me as I don't need to wash my hair every day.